Universal WAS made by ADI until they had that line catch fire. It was then contracted to General Dynamics in Canada. Which is now manufacturing the powder for the 155mm Artillery Shell. All of the Clay's series of powders are out of production due to this and it's been going on long enough that it's return may be questionable. Alliant has also been having major issues because obtaining Nitro Cellulose has become beyond difficult. It's why Unique is out of production.
As a result we live in a world of finding alternatives that work. I shoot Competitive Skeet to the tune of going thru 15,000 primers per year.
12 Gauge. Lots of alternatives for the 12 gauge, all of which are denser than Clays so plan on using 3/4 and 7/8 ounce wads to get a decent crimp. Also plan on these powders shooting dirtier, which really isn't a real inconvenience because you really should clean your barrels after 100 rounds shot. Fail to do than and you'll have chokes clogged with plastic from the wads.
20 gauge. A couple of good alternates here, some of which are off the books but have been tested, check on Shotgun World. I like to use Longshot because it's proven to be so consistent, a friend I shoot with like 572. He claims it's cleaner but I have compared the two and found no difference at all in cleaning time. My pet load for the 20 is 15.4 grains of Longshot with a 3/4 ounce charge of #9. I've also loaded 16.0 grains with 7/8 ounce loads but shot is expensive and only load the heavy's for Sporting Clays. BTW Hulls are Remington Gunclubs.
28 gauge. Again Longshot and 572 will work well. Crimps will be dished with either powder unless you load with the Winchester AAHS hulls. I use Cheddite hulls for the 28 gauge and while the crimps are dished they are consistent and function perfectly while lasting twice as long as the AAHS. Powder charge with Longshot is 15.4 grains, the same as what I use for the 3/4 ounce 20's.
410. The biggest issue with 410 is finding hulls, you will not pick them up at the range. My preferred hull is the Cheddite hulls because they outlast the AAHS by double. However the supply is very spotty and I have Fiochi hulls on hand as a backup. Fiochi hulls are low volume hull and the only powder that will fit a full 1/2 ounce load is H110. So that is my goto for the 410. Also have an 8 lbs. keg of 410 powder on hand but it's too bulky for the Fiochi hulls and even dirtier than H110.
20 gauge.