I had purchased ones online that were slightly larger in diameter and shorter cutting length for around $17 each at www.bitsbits.com
Then I discovered the ones I am using now LOCALLY for $5 each. They are .003 smaller diameter and cut 25% deeper. Google Sparktech Inc. in Round Rock, Texas. They dont seem to have a website for e-commerce but you could probably call them and see if they would mail them. As small as these are shipping should be letter rate and as cheap as they are I would order a hand full of them. I buy three at a time but I also can drive there in 10 minutes.
Speeds and feeds...cant remember off the top of my head speficaly but spins at 18k and feeds rather slow. Makes 10 passes starting at .010 and going .010 deeper each pass. Takes a while to cut them but that is necessary to not break bits. At .021 you probably get the flu shot with a bigger needle.
I could email you the cut files if you like. I created the cuts in vcarve pro and converted them to shopbot code. At the very least you could see the machine code and convert as necessary.
I am definitely not saying this is the best way to do this. If you have access to this kind of gear its definitely a way to cut the slots dead on. I did it this way cause I could. Alternatively I could have just sent any a couple blanks to LMI and had then slot and radius them for like $18 each.
Its definitely not a bad way to cut the radius...way less work than the old router jig method. Again, cause I could though. Without access to the shopbot I would mail it to LMI for slotting and radius. PM me if you want these