North Korea has a ton of older artillery platforms which still have application in Ukraine - but don't actually have the range to hit Seoul until/unless they pushed in an offensive (which would leave their artillery exposed in the open to get it in range). However North Korea has been developing and producing stuff like the KN-09 (
https://en.wikipedia.org/wiki/KN-09_(multiple_rocket_launcher) ) which has range and damage - though from everything I know not a precision weapon despite the guidance - they'd rely on just barraging Seoul and/or the area of command centres, etc. with it rather than being able to pinpoint military targets. The last few years a lot of their resources have gone into producing them but actual numbers are unknown.
It is possible NK might sell off a lot of its older artillery to Russia to put the resources into its newer systems as the biggest advantage they have is the ability to threaten Seoul with massive bombardment.
Ultimately a lot of NK's military hardware relies heavily on China but I'm not sure there is directly a backdoor for supplying Russia there - China seems quite leery of getting involved militarily and it benefits them almost as much as the US to see Russia bleed aside from the aspect that Russia adds additional strength on the international stage to counter the US.
One of the ways they are dealing with that is who gets equipment - they have quite distinct lines between territorial forces, security forces, professional army, etc. etc. and can divide out who has what and their respective logistics.
