You can check the site sponsors for parts and service.
Here are some answers to your questions based on my experience:
1) Mister John Auto (Weston and Steeles area). I always take my car there, they are really good.
2) There is someone on Kijiji selling aftermarket M bumpers, also in Weston and Steeles area. I have no experience with them. Search Kijijii.
3) Check Ebay.
4) Check site sponsor list.
5) Don't know
6) When I got my bumpers I went OEM because I didn't want to have problems with the fit. It will obviously be more expensive. There are alot of other parts that you will need to complete the conversion.