While I personally believe that Russia is supplying them, I have to disagree with that statement, the civil war in Ukraine is basically like a fight in a gun store, the are massive caches of weapons and ammunition in the numerous bases.
Added to that, this isn't some small scale thing, this incarnation of the republic of donetsk may be significantly smaller than before it was merged with Ukraine, but the DPR and LPR combined are 82% of the size of Wales and have the same population, it's a big area.
No offense but I find this far fetched.
The logistics alone would be HUGE. Just think about it for one second, we are talking tons upon tons of Fuel & Munitions every day. Tons upon tons of Grad Rockets & Artillery Shells per day required at multiple fronts needed. Not to mention the endless list of other support needed.
Granted They might have captured stockpiled kit. But no way they would have the Massive logistics required to deal with it. What about the millions it must be costing every day? who's feeding them? Remember the money is not coming from the Ukraine government.
A constant stream of tons of Fuel trucks would be needed feed those T72s let alone parts,low loaders,mechanics,support.
You can bet most of those fighters are being payed.
Remember when this first kicked off they were interviewed. They had very little. They stated that if the Ukrainian army turned up they would probably just surrender. Remember the rag tag checkpoints & makeshift weapons. Night and Day within six months.
It must be the fastest turn around in history, they suddenly have the huge numbers, training, anti air, tanks art,MLRS,drones,communication jamming kit,radar,logistics it goes on and on. To beat back a professional Ukrainian army i.e. turned the tide within a month.