I've tried a few but the problem is that you can either have cake makers who ice cakes or biscuit makers - you tend not to get people who are prepared to ice biscuits.
Sorry the above post was meant to be a pm in return to your's. I was so cold from just coming in from the football I went a bit more loopy than normal.
I don't think I've ever seen an iced biscuit. I have seen some iced buns though that look like they've been done with a "pre-printed" circle of icing. Whoever makes those might be able to do biscuits. Unfortunately I can't remember where I've seen them