I have kept sheets of stamps in a stock book for many years and have not had a single sheet stick to the glassine pages. So, based on this experience, I would suggest inserting a large piece of this material behind the sheet. Another possibility would be a piece of waxed paper.
If you live in a high humidity area, the stamp adhesive is prone to stick to anything made of fibrous paper. Any stock that has a semi-glossy surface would be more applicable.
I would think almost any stamp supply dealer would have them or be able to get them. A little hunting on the web should produce several places. Then again, like Wooden Jefferson said, any semi-glossy surface would work, so you might want to consider good old fashioned wax paper from the grocery store or velum from a graphics supply store.
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Matt
Mike
Lafayette Grading Set
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