Why not get a feeler gauge from an auto parts store? It's cheap and easy to use, not to mention readily available.
Nice thought, but they do not give an accurate reading. You need to stack a bunch of them. It does not tak much to be off by .010".
The Fowler gage is good. But he may not be selling them anymore. Any Machinist could make you something similar. The dial gage Fowler uses is usually from Harbor Freight. The metal parts are custom made.
You can use a set of (inside) calipers to measure the distance between the tip and a a flat piece of glass or metal held against the table. Digital calipers are easier to read. There are some inexpensive ones at Micro-Mark.
There are some other do-it-yourself gages shown in the photo area of the Mouthpiece Work Yahoo Group site.
I use a Machinist's depth gage with a 6" base. The standard 4" long base is too short.