for my 1900 hammer, I ended up with a 1904 forend that fits and works fine, and I had picked up some others that didn't work out (either my own mistake, or mis-information from seller). I learned a lot along the way, and this is an awesome forum, so I'll offer them up here. prices are just what I paid for them.
1911 - $88, s/n: 335677, 12 guage. tiny spring that lifts the foreend spring out of the slot is broken, but main spring is fine. wood checkering worn flat on one edge, and there's a small dent in the wood as well. no engraving. 00 grade I think.
1926 - $149, s/n: FW 90426, 20 gauge I believe. it's narrower that the other 12's I found. checkering is worn, wood also has some deep scrape marks on one edge,
1919 or 1947 - $100, s/n: 14023 D, serial number is also hand stamped into the wood on this one. checkering really worn on this one. not an extractor type forend. the barrel lug slot is really narrow. engraving on metal.
I can provide pics if you are interested. located in Iowa.