Those bushings are about elusive as unicorn horns. I know they are out there for the rebuilders, but parts sources for them are protected like the Crown Jewels. Your 73 302 should have a single upper bushing. Ford actually used upper and lower bushings through 1969. Ford said the lower bushing was not necessary, while others said it was just a cost saving move. Very few were ever sold at the dealer/shop level. It was cheaper to install a rebuilt distributor with a better warranty than to incur the cost of shop labor hours plus the cost of the part.
The part you need is B8QH-12120-A and is of course long discontinued from Ford. There is a site
http://www.rearcounter.com/B8QH-12120-A-parts181898.html that post parts for different company's. I would try Dennis Carpenter first and let them know where you found the listing. Hopefully they can help you as they are pretty deep into Ford's and restoration parts. Good luck!!
