Something interesting I've seen recently is 'mini-rail'. The buttons are tiny, much smaller than standard rail buttons.
I've also seen a hinged rail (not sure if it was mini-or standard) which folded in half, either for small stuff or storage/transport.
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Colin makes buttons which are like a mini version of the normal rail buttons, and also a nice guide which is like a mini-version of the ACME rail guides, but milled out of phenolic (Tufnol) sheet.
May be of some interest, overkill perhaps for really small stuff but for MPR?