I have an old Skilsaw circular saw, model 526. It uses 5 7/8 blades with a diamond-shaped arbor. As of yet, I've been unable to locate a blade of this size, much less a hollow ground planer blade which is now worn beyond possible repair. Can anyone point me to a source for blades of this size and type. The current blade is an Oldham Saw Co. P/N 578-C-H.C which doesn't seem to cross to another manufacturer's part number. Thank you in advance for your help.