Certain nurseries only sell roses grafted onto fortuniana. The ones that don't specify the name of their rootstock probably aren't using fortuniana.
If you have to order online, your best source would be K&M Roses, which carries a highly impressive variety of roses, all grafted onto fortuniana.
http://www.kandmroses.com/
Nelson's Roses, a wholesale nursery selling roses grafted onto fortuniana rootstock, does not ship its roses by mail, but it delivers roses to many local nurseries in Florida. If you're close to any local nurseries, you could check for Nelson's Roses there.
http://nelsonsfloridaroses.com...
Here's a list of the local retailers carrying their products:
http://nelsonsfloridaroses.com...
