At the risk of some criticism, might I suggest that you follow a regime which has been adopted for 4000 years or more- and learn to use simple tools to make your own tools.
In this instance, you need a scraper, a bit of wood, a handfull of tacks and Engineers blue/Dykem or even a waterproof black felt tipped pen.
Not a lot more. You use a flat reference surface - perhaps on your lathe and remove the high spots that are revealed by rubbing the inked surface against the flat surface by moving the gib back and forward perhaps 4-6 millimeters. You will find where it fits and where it doesn't. This is why people are called- in English 'fitters' You remove the high spots which are revealed, clean the ink off and re-ink and REPEAT. Eventually if you have done it right, you will be left with a surface of bright scrapings all across the gib.
It's as simple as that. It is the basis of ALL engineering- Removing metal that should not be there.
Regards
Norman
