I have been hobbyist for couple of years. I am polite, respectful and understanding with lovely ladies I am with. and I had the opportunity to meet great providers during this time. Lately, I have been wanting to experience a 3some with another provider and a hobbyist. What is the best way to request this to a provider, without affending her? Will any provider be interested in an experinece like this?

That is something you should bring up with her when you see her or if you have seen her on numerous occassion then I think she will be ok with it if you email her with that question.  But I would do it before your visit ends that way you know what her boundaries are.  Take care and have fun.

There are also some providers who would love this.  If you are a VIP with some established review history, PM me.