The JIS Screwdrivers are mentioned in several topics in this Forum. I discovered several years ago that I could make a perfectly satisfactory substitute by grinding a small amount from the tip of a Phillips cross-head driver. This "small amount" is ground straight off the tip; i.e., perpendicular to the shaft of the driver.

The "correct amount" varies with size (and with the quality of the Phillips driver, sometimes), and is approximately: 

.010 for a  #0 Phillips
.015 for a  #1 Phillips - and
.030 for a  #2 Phillips

I don't think anything larger is used in model engines, and as noted above - - You may need to "sneak up" on the exact amount of material to remove.

$$ is less an issue now, and I have purchased the Real Thing, but the budget approach works pretty well, too, if $$ is tight.