most should fit including a few single shot forends.... I suggest you take a few nice pictures of the gun especially the bottom where the forend should be. it would be easier for someone to help you if we knew exactly what we were working with.
I've had good luck with Lee's Gun Parts in Dallas Texas area. http://www.leesgunparts.com/ Does not do anything online really, and hard to catch on the phone, but have had great luck dealing with... more
Any of the 24C variety forends will fit. If your looking to keep it true to the original, Series M, N, & P all had the same round toothpick style forends.
the easiest way for me to post pics on the internet is by using a photobucket account. you upload pics there or on facebook and then put a link to the picture in your post. like so Don