This appears to be a Dutch florist rose.

I would ask Longwood Gardens where they got theirs.

Here is a link that might be useful: Tombola @ helpmefind

The only place I see listed is in the Netherlands and it is listed as a florist rose like hoovb said. Longwood may have imported it, which is a very involved, lengthy and expensive process that they would have the resources to do. It's fairly new and patented so I doubt you'll find it available anywhere here.

Helpmefind.com shows two roses by that name, one a floribunda and one a hybrid tea. Can you describe the one that you saw? Perhaps we could recommend something similar. I won't get to Longwood until early June.