@vid1900 I spent a few hours yesterday at a automotive paint supply (pretty much the only decent one left here, FinishMasters) near San Francisco, California.
I figure I'd share what I learned here in case there are California folk interested in getting their hands on clear coat.
The typical auto parts stores aren't selling anything even close to quality clear coat or paint products, and I've checked them all. Even with FinishMasters, I had to go to more of a central hub to get access to decent inventory.
One interesting tidbit is that it is now apparently illegal to buy/sell PPG JC660 (or, as you say, it's cousin Omni 161) in California. I believe the current product name for that is the Omni MC161 High Solids Urethane Clear...They still make it, but I'll be damned if you can find a jug of it in California. Omni/PPG make a line of clears and paints with the code "VOC" (stands for meeting the standards for Volatile Organic Compounds) that meet the newer regulations, so you can only buy these VOC coded products. My sense is that they were selling 161 as part of their inventory until it was gone, which seems to be the case everywhere. They have various universal VOC clears of various brands, though when describing the types of clear coating we all do here, they admitted the JC660 would have been way more forgiving (particularly on something laid flat). They used the term "spot clearing," which I guess is a thing that JC660 is often used for.
This is what we settled on, Omni MC760, is a "universal" VOC 4:1 clear, though no question it has different characteristics than the JC660.
Anyone ever used this stuff? I'll report back our experiences with it. I'm not sure it's hard enough for a playfield, but I'd love any thoughts on this. For the technical folk, here is the datasheet:
For this clear, you need to sand the base coat if you wait longer than 24 hours after the base coat is applied before shooting. They recommend 5-10 minutes between coats of clear, and 4 hours before it resists masking tape, and around 16 hours of air-drying before you can sand or polish it.
The OneChoice SLV4985 is a flattening agent to bring down the gloss if you want something more like a semi-gloss or matte clear (which we will be doing for our cabinet work). They recommended only using the flattening agent if you plan on covering everything you want to coat in one pass from one mix, because it's apparently super hard to get consistent mixes. Also, you can't sand/buff a flattened clear, so it's obviously only useful for cabinet work.
All of this stuff is wicked expensive and you really want to do more research than I did before you jump in.