any camera shop that repairs bessa's can repair that part of the r-d1, but if you really busted the front prism that's going to be an expensive repair - you're looking at around 450$ or the GBP equivalent. most shops just replace the whole RF module in such cases as it's a real pain in the neck to remove, replace, calibrate and re-cement the new prism.
if you only busted the plastic covering that's attached to the top housing then you're lucky and you could probably have it repaired for nothing but the labor cost, it's just a piece of thin plastic.