Stem Needed for a Amphora X-tra 721

If you want to buy bulk stems and fit them yourself here is a link, http://www.pipemakers.org/ for the Pipe Makers Eporium. Lucite stems can be purchased individually, vulcanite by the dozen.
One problem you will have is the stem tenon is not cut to a precise size. So you will have a few choices on how to fit the tenon to the existing mortise.
1. Purchase a tenon cutter, available from the attached link. The problem is they are not cheap and require a lathe.

2. Forum member darjonenes, explained how he inserted a next size larger drill in the draft hole at the tenon, chucked up the drill bit and used sandpaper to reduce the tenon to the proper size. I have used this technique with a drillpress and a shear file with good results. Check often with calipers.

3. You can find video explanations on youtube on how to remove the tenon and insert a derlin tenon. This will require a drillpress. Derlin can be purchased online. Amazon, ebay and other sources are available.
If these options are not for you than a good pipe repairman, as suggested above would be a good choice.