Since my name was mentioned I thought I would enter the fray 
Yes I have two San Ace 38mm fans which I was lucky enough to pick up from Ebay for £7.50 each.
They are indeed hard to source and if your look at the San Ace catalog in China you will find they make about 20 different 120mm 38mm fans with different specs/cfm/air pressure.
I have indeed got them running on a fan controller and for general browsing/word processing they can be set to 3v/4v (or even off!
) and everything stays fine (all speedstep etc gubbins switch on so when browsing my cpu is running at only 3Ghz and lower volts). At 3v/4v they just rotate very slowly and are silent but at least puts a little airflow through the rad.
I can also confirm that at 12v they are indeed loud. lol. However, the performance is amazing. The airflow through my rad out of the top of my case at 12v is good enough to dry your gf's hair with.
Tbh I only use them at 12v for silly benchmarking on hwbot with my cpu at sill 4.9Ghz levels. For gaming I just turn the dials up slightly to perhaps 5 to 7v which although raises the volume levels slightly, you can't hear them over the game.
For Info my fans were the following models:
Sanyo Denki San ACe 109R1212H1011
Fan Size: 120mm x 120mm x 38mm
Speed: 2600 RPM
Airflow: 102.5 CFM
Noise: 39 dBA
Static Pressure: 64.7Pa (~6.6mm H2O)
Bearing: Ball bearing
Voltage: 12 V
Current: .52 Amp
Power: 6.24 W
At 6v they are quieter than my xilence redwings were on 12v put push way more air through my rad.
Temp difference was a 3c drop under IBT at 5v and a 10c drop at 12v compared with the xilence on 12v.
Interesting comparison here which shows how badly some good cfm fans perform through a radiator as they don;t have sufficient static pressure.
http://www.madshrimps.be/?action=get...36&articID=936
Full product list here:
http://db.sanyodenki.co.jp/product_db_e/coolingfan/dcfan/cooling_dcfan.html
The 9G replaced the 109R AFIK. 9G1212H1011 can be bought new in the uk for around £15-£16 each. Specs are very similar but cfm down slightly (99cfm) but static pressure up to 7.2mm.
There are two very similar ones for sale at £7.99 each on Ebay atm.
http://cgi.ebay.co.uk/SANYO-DENKI-1...K_Computing_Networking_SM?hash=item35a68f8352
EDIT: San Ace have high ampage and don't work with all fan controllers so make sure your fan controller has enough juice down the line.

Yes I have two San Ace 38mm fans which I was lucky enough to pick up from Ebay for £7.50 each.
They are indeed hard to source and if your look at the San Ace catalog in China you will find they make about 20 different 120mm 38mm fans with different specs/cfm/air pressure.
I have indeed got them running on a fan controller and for general browsing/word processing they can be set to 3v/4v (or even off!

I can also confirm that at 12v they are indeed loud. lol. However, the performance is amazing. The airflow through my rad out of the top of my case at 12v is good enough to dry your gf's hair with.
Tbh I only use them at 12v for silly benchmarking on hwbot with my cpu at sill 4.9Ghz levels. For gaming I just turn the dials up slightly to perhaps 5 to 7v which although raises the volume levels slightly, you can't hear them over the game.
For Info my fans were the following models:
Sanyo Denki San ACe 109R1212H1011
Fan Size: 120mm x 120mm x 38mm
Speed: 2600 RPM
Airflow: 102.5 CFM
Noise: 39 dBA
Static Pressure: 64.7Pa (~6.6mm H2O)
Bearing: Ball bearing
Voltage: 12 V
Current: .52 Amp
Power: 6.24 W
At 6v they are quieter than my xilence redwings were on 12v put push way more air through my rad.
Temp difference was a 3c drop under IBT at 5v and a 10c drop at 12v compared with the xilence on 12v.
Interesting comparison here which shows how badly some good cfm fans perform through a radiator as they don;t have sufficient static pressure.
http://www.madshrimps.be/?action=get...36&articID=936
Full product list here:
http://db.sanyodenki.co.jp/product_db_e/coolingfan/dcfan/cooling_dcfan.html
The 9G replaced the 109R AFIK. 9G1212H1011 can be bought new in the uk for around £15-£16 each. Specs are very similar but cfm down slightly (99cfm) but static pressure up to 7.2mm.
There are two very similar ones for sale at £7.99 each on Ebay atm.
http://cgi.ebay.co.uk/SANYO-DENKI-1...K_Computing_Networking_SM?hash=item35a68f8352
EDIT: San Ace have high ampage and don't work with all fan controllers so make sure your fan controller has enough juice down the line.
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