Well, the OEM flasher appears to be a Tung-Sol P273D. After searching for this flasher, I discovered several references to the Ideal 222 flasher being a replacement. So far I haven't found either one for sale.
I tried a BUSS 550 flasher, and it didn't work very well..... the signa;s flashed just fine, but the indicator lamps in the dash wouldn't work. After working with the flasher's guts, I was able to get the opposite indicator to flash in the dash.... then after a little more tweaking, BOTH dash indicators would flash at the same time.
I'm heading to the salvage today, and I'll see if I can grab a flasher out of the '59 Buick I have been eyeballing.
1960 4 door Dynamic 88 sedan