Try "googling" the various seed companies on the net.

Holes Greenhouse in Alberta have many to choose from.

Here is a link that might be useful: Holes

Thanks C.G. Hole's do have a couple that I don't have, I'm always looking to add to my collection. It's getting hard to find a source to buy perennial asters. There are a few I have weeded out as they turned out to be to too invasive for my likes, but most are well behaved and pretty much stay in clumps.

A......

I TOO COLLECT ASTERS AND THIS YEAR I PUT IN AN ORDER FROM LILIES OF THE VALLEY. SORRY I DON'T HAVE THEIR ADDRESS BUT IF YOU CLICK ON GOOGLE IT IS RIGHT AT THE TOP. THEY SENT LARGE PIECES OF THE PLANTS ANDTHEY HAD SOME I DIDN'T HAVE.

It's not new but I love the bright blue colour of Stoke's Aster 'Blue Danube'. Vesey's has it in their spring catalogue.

I don't know if you have them already, but Veseys has Pinkie Aster and September Ruby seeds

Here is a link that might be useful: Veseys Asters