I expect the pellet sizes are listed on the bag. Although my feed store takes special orders they only commonly stock generic sizes and/or brands. However, all feed stores get weekly or bi-weekly shipments and it should be no problem.

My opinion and it may be worth just what you are paying for it: Unless you are raising fry that need tiny feed and/or doing something exotic, most commercial 32% protien feed will work just fine. The darn stuff softens in water and the small fish chew on it. Just make sure it is fresh. All bags should be dated. Old feed loses its food value and as it dries becomes more sinking than floating. This is more of a problem in the late fall than spring. I mostly use Purina GFC or Aquamax. However, in the late fall the feed stores are closing out their old stock and I sometimes have to change over to Moormans or some other brand. As long as it is not over 3 months old, it seems to work ok. The fish eat it and thrive. If you have questions, most feed stores will cut a hole in the bag and let you examine it. Then they will tape the cut place. Smell it and also feel for oil content. You can tell the difference in old and fresh stuff. The kicker is that the Premium brands and the off brands cost about the same. So, I try to stay with the good stuff. Heck, it all smells like chicken feed.

From the Purina Aquamax handout, here are the pellet sizes and other info by Product Code:

5D00 Powder Sink 50% protien
5D01 .8mm Sink 50%
5d02 1.2mm Sink 50%
5D03 1/16 in. Sink 50%
5D04 3/32 in. Float 45%
5D05 3/16 in Float 41%
5D06 1/4 in Float 41%
5D07 5/16 in Float 32%
5D08 3/16 in Float 32%
5D09 3/16 in. Float 36%

Other info in the bulletin includes amount of fat and fiber in each.