Any recommendations for cleaning the stainless mesh on flame arrestors to get them to like new condition? Over the years they have experienced some discoloration. Can they be painted if necessary? Any guidance or recommendations would be appreciated.

Use a degreaser like simple green or if its really dirty use some carb cleaner first.

Just what Griff said.

If you have one of those "buffing balls" for your drill (no comments please), you can try applying some FLITZ or Mothers Polish to get some shine back. Just make sure you have an air compressor to blow off everything VERY well before you re-install (polish, dust, cleaner, grit, dirt).

Brake cleaner has always worked well for me. Obviously if using a cleaner be sure to use it on the workbench and well-ventilated area . As for the shine...sounds like others have given you good advice already as well. Local metal fab. shop or HVAC might have capability for polishing and do it reasonably also.