You could try Swift Greenhouses. They do plugs in 50 cell trays although most of these are perennials. Germania is a broker for them and their min order is $300 or else pay a $20 processing fee. So you'd be looking at that plus shipping costs.
Most of the plug suppliers who do cuts, put the flowers in 128 / 200 / 210 / 288 cell trays.

Amaranths - Celosia (Sylphid and Kurume have short crop times) - Purple Majesty Millet
Cheers Kim - BFFF

Kim - I was interested in your comment regarding Sylphid Celosia, as I love to use in arrangements with zinnias. I started a few seeds in the spring and am using it now, but wonder how it behaves if planted now (early August); our first frost is usually mid November - I'm in Florida's zone 8b. Do you have any experience with starting it late summer, and if so, do you direct seed or transplant?

Anndi
Sylphid is awesome with Zinnias. You can plant plugs of Sylphid during August and they should flower well before your first frost. Note that the later you plant them, the shorter they may be. Yes I transplant, plugs need to be at least 4wks.
Cheers Kim
Billabong Fresh Flower Farm