Any suggestion on how to go about doing this?

The present brand of maple wood floor that I am putting in doesn't accept the "standard" oak splines that I can buy from a flooring company here in town. My older wood flooring took it no problem. In this case, the splines are to wide and a little too thick.

To get them to fit now, I'm putting the spline into a long piece of my old wood floor in which the spline did fit and ripping with a table saw about 1/8 off the width. Then I hand scrape the spline (using a plane) to a lesser thickness. It's not hard, but it takes a while longer than I would like.

Any suggestion on how to make my own that would be faster?

Why not try 1/4" plywood? Or masonite? Then simply rip to desired width. But check that 1/4" will work BEFORE you commit to ripping those splines. Now that flooring is being shipped here from all over the world, the old NOFMA milling standard no longer applies to many non-American made brands, which means we have to make our own splines/slip tongues.

Great suggestion. Thanks. I don't need to worry about rounding them or anything do I?

I'm putting down quality stuff from a well-known and well-liked Canadian brand, but it obviously doesn't conform to the NOFMA standards you mentioned. At least it's not a serious problem.

Yes, many Canadian brands have different T&G profiles than the American counterparts. And even some American brands that are not NOFMA members use different T&G profiles. For the most part, Canadian flooring is equal (and in some cases, superior) to the best American-made flooring.