How can I mount a 25.4 mm seat-post on a frame that needs a 27.2 mm seat-post My bike has no rear suspension. So I thought of putting a suspension seat-post on it. Unfortunately the only suspension post available in my city is a 25.4 mm one. I have added some scrap metal to fix it for now. But it's still a little wobbly. What is the best way to do this ?
There are seatpost shims available for a few dollars. You should get them easily in your local shop or online.

I use an aluminum shim in one of my bikes with exactly the dimensions you need, it works flawlessly and looks very clean. I got it for about 3.50 € (5$).