10" spindals

http://ssbrakes.com/commerce/detail/index.cfm?nPID=8558

That is the link to the disc brake kit i want to get on my car. heres the catch. my car, a 70 dart, is a /6. so from what i understand, i must have 9" drums. that kit bolts to 10" drum spindals.

i guess my question is, where can i find O.E. 10" spinals and how much should i expect to spend?