Stihl 23RMC or RSC x 67 drive links is what was supplied with your saw. Oregon 20 semi or full chisel will also fit and work well. Gauge seems to be a regional thing, we get very little call for Oregon 22 series so don't stock it. The semi chisel is faster in clean or frozen wood, the round top chipper chain is more forgiving in dirty conditions.
Yes the dealer said that it's pretty much only 050 bars around here. The saw did come with an rsc chain. At $40 from the dealer I'll be getting a few oregon chains to try first.
The saw has a yet un-identified stihl chain on it right now. I will post some pics to see if it's salvageable. Might be a good project for my granberg jig when it arrives.