Mr. Goat's comments are obviously focused on stock checkering tools.
If you are referring to a metal checkering file ... like the ones used for bolt knobs, hammer spurs, backstraps etc., you
might try Grobet Files of Canada ( 416 293-2474 ). Grobet makes a line of metal checkering files in 25, 30, 40 & 50 lines per inch.
I think they're called Swiss Vallorbe files. Guessing that they may be the same as, or very similar to, the ones supplied by Brownell's. Try their (Grobet's) part No. 131.040 as a place to start .... The checkering file establishes the spacing from a "master line" by advancing the file by one notch at a time ... lines are then deepened by using a standard 60 degree needle file.