you can just make them yourself too, most folks I know do this.
All you need is a cylinder that slips into the head when the rocker assy is off, to block the oil up to the rockers. Then, drill about a .090" hole in that part, and slip it in, make sure it is below flush so it doesn't interfere with the rocker stand fit. Try to design it so you can get it back out easily.
You can also use a #90 or so Holley Jet, some folks go even smaller.
Are the rocker shafts or rockers worn? Sometimes that will cause a lot of oil up on top, the restrictor is an ok crutch (I've done it) but new rockers/shafts might help too.