There is a member in the Mamod forum that may be able to help you if you only need a few:
Oval style decal as found on the Old Hobbies vintage stationary steam engines usually situated on the base plate.
1 x Quality Waterslide decal with instructions.
Chris (flywheel61) has been supplying decals for years, however he is in Australia and the postage is prohibitive to America so I believe he has arranged with Alan to distribute them.