Clown plec's get around the 3 - 4 inch mark, Ancistrus stay get around 4-6 inches. L002 gets to be about 3-4 inches, L307, L270,L46 stay quite small under the 5inch mark of there abouts, there are some great small plec's about, Some of the big ones like sailfins need plenty of room, i have a 12 inch sailfin(gibbiceps), they can reach upto 24inches, same as common plec they can also reach the 20+ mark. Always choose the plec carefully, never go in to a et store and buy the first one as you may end up with a biggie if you unsure of the species. My local has a lovely red plec about 18inches! a little too big for me but oneday lol
anyway hope you find some! Clown plecs need company the more the merrier to keep them happy i got 4 in my tank moment about the 2.5-3inch mark and doing well!