Nobody that I know of makes a 37mm chalk round commercially.  If you did find them, however, you would need to register your 37mm as a DD.  "only" flares, smoke and other signaling rounds can be used out of a 37mm without DD'ing it.  I registered my 37mm and got a spare tube which I had bored out to 40mm so I could use Chalk Rounds.  I also have a 40mm BeeHive round I use out of it.

MadDog

After doing a bit of searching on here it seems like it all comes down to INTENT.

Flares are not INTENDED for launching at ground targets.  Could they be?  Sure, if launched at a PERSON then that person would get charged with using and possessing an unregistered DD.  (Anti-personnel)

Chalk MARKER rounds are INTENDED to be fired at ground targets and marking the impact.

Not signaling.  MARKING.

That's about all I gathered from a quick search.

Damn BATFE - a person NEEDS a lawyer to figure out what the hell their INTENT is from their decisions & rulings!

~Will

There is no such animal. Only 40MM rounds that use orange dye for marking round impact.

The exception for flare launchers provided in the NFA specifies flares, smoke, and gas, or line launching. It does not exempt 37mm from DD requirements for ANY other ammunition, specifically anti-personnel ammunition.

Since there are no commercially manufactured "chalk" marking rounds in existance, the question about them being covered by the exemption has not been answered as of yet. IMO, if you desire to manufacture this type of ammunition, write a letter to ATF FTB, and ask for their ruling. Don't take legal advice from an internet forum. GROG