e-Gunparts.com
gunparts.com has them
cowbourd
At Gunstocks Inc.
Look in the yellow pages for gunsmiths.
See related link.
Try Numrichgunparts.com
http://www.e-gunparts.com/DisplayAd.asp?chrProductSKU=68020&chrSuperSKU=
No one.
http://www.gunstocksinc.com/web_pages/Plate-pics/Ithaca-Stocks/Itaca-stocks.htm
The model 5100 Stevens shotgun has a plastic stock
Check with numrich gun parts corp. or look at E-gun parts.com
Try e-gunparts.com or any on the stockmakers you can find by doing a internet search on gun stocks.