Where can I find an ac/heat blower motor relay (64 GTO)?
 

Does anyone here know where I can find an ac/heater blower motor relay for a 64 GTO? (See attached pics of the old one).

I’ve been looking, but haven’t found one yet. Thanks..

Doing a quick search all I can find are ones that have 4 prongs instead of the 3 yours has. Year One list on for the 64 but again the picture shows 4 prongs. It may be a stock photo and not correct but I'm sure a call to them and ask if they can look at to make sure it matches would be OK.
https://www.yearone.com/Product/1964...nr#prettyPhoto[part]/0/

The other thing I found is a horn/ power window relay that looks like yours. It does say "1957-72 GM; Multi-Purpose Relay; Various Models; Horn; Power Windows
Reproduction of the multi-purpose relay designed for use with various " I wonder if it would work on the AC motor??
https://www.ecklers.com/gto-horn-or-...lay-hr614.html

There are several aftermarket relays that will work.
 

As pointed out by jwcfbd, that style was used for several different purposes.

Here are three relays that interchange with the OEM part number 9775028 that are available on RockAuto.

Four Seasons #35770 $33.79

Standard #RY-7 $23.79

Wells #1R1990 $31.79

All plus the standard shipping charge and sales tax.

Looks like they interchange with 1968 Cadillac Deville blower relays.

Other OEM GM relays that interchange are 1115870, 1116959, 1116990, 1496721

The OEM number also show interchanges to 176251, 19189334, 2790HV32156, 35783, 53087, 9775028, KB220715

That 1968 Cadillac application might help you find one locally.

Good luck!