Can anyone tell me where I can find a forend for a double barrel 12 ga?

Try Boyd's gunstocks. You'll need the original forend iron. If you don't have that, makes it a little more challenging.

5100s were made for a long time. If you can't find one at the various replacement stock makers, REALLY search the web by looking at all the auctions sites and putting a WTB ad on ALL the gun discussion sites. Keep trying; one will show up or a really nasty parts gun with a decent forend will show up. Buy it for the forend and resell the parts. Make sure that you specify which forend material you need: walnut or the funky plastic Stevens also made. It would also be worth while to ask on our Savage Collector's forum if the 5100 forend will interchange with one of the various models of the 311. Those are even more common.

The way I understand it is this; there is no Stevens "Model 5100", that was the part number of the action that was used for Springfield shotguns (economy division), the Stevens 311 series (standard division) and the Savage Fox Model B ("upscale" division). With the exception of very late guns (mid to late 1970's), the forearms should all interchange (with perhaps some minor fitting). I learned a lot of this from reading the postings of Researcher at Shotgun World. I have a couple of old (early post WW-II) Springfield by J. Stevens Arms Company shotguns (a 20 and a 12), when I examine the forearms they look like they would pop right onto a Stevens 311 shotgun.

Here's a link to a Stevens 5100: http://www.gunsamerica.com/94384168...5100_12_Ga_Double_Barrel_shotgun_USE.htm

Here is one of mine, a 20 gauge. This one was bought by my Great Uncle Alvin, a farmer, from my Grandfather, who owned the local hardware store, in 1945. My cousin gave it to me a few years ago - it had been in the packhouse for 40 years and was in miserable shape. Between two gunsmiths (one glued all the stock cracks, the other polished the bores and installed new firing pin springs) and I reworked the stock and fitted a new buttplate. It looks pretty good now and is one of two I own (the other one is a 12 gauge that I hunted with as a boy, it was from the estate of another great-uncle.) They are tough old guns and worth working on to keep in firing condition.

The Stevens 311 is the same as the 5100, just changed names after WW II. At least that's what I read.