They are still available, I'll send you a PM
Hornady has a chart on their site which tells you which Pistol Powder bushing to order for the powder charge that you want, but it does give any idea what size hole you would need.
http://www.hornady.com/assets/files/handgun_pwdr_meas_chrt.pdfThe Lee AutoDisk instruction sheet has a chart which shows the hole volume in CC's that is needed for a particular charge. With that information you can calculate the hole diameter you would need in a 1/2" (or other) powder slide. Tell me what charge you want and I'll give you a sample calculation.
http://www.leeprecision.com/cgi-data/instruct/AD2302.pdfIt's best to drill the hole undersized, than ream it to the desired size. The best tool is a Taper Pin Reamer of the appropriate size. It has just a slight taper. That's what Star used on their powder slides.