Oh, it is really pretty! Are you sure you can't find that purple fabric? Well, I asked because I thought I had some, but mine is a bit different. I'll attach a picture anyway, in case either could help at all.
Maybe you could find a similar fabric to what you have....and I think your purple is darker than mine...but if you just found something about the same color and then made blocks out of it and your white, then you could have the outer blocks be out of them, all the way around. So you would end up with the 8 x 10 block arrangement you wanted. It might look good...sort of a border, but still with white blocks?
Anyway, that is my idea. Or Audrey's idea of one fabric with green and purple and white is a good one too.
Pretty quilt though! Good luck with what you decide.
Dina