They are attached to the heat sinks (2 on the SA800. There are makeshift homemade options but even the best do not replicate the diode response of the original. Occasionally there is someone who pops up with “hey I have some” but in my case, the SA800 was sold “as is” to a parts house.

The wire connections to the diodes get very brittle. So if you are in there doing anything (clean up, recap, pot deoxit) and bump a wire they will break. They are impossible to find and many “try this” options but nothing short of replacement diodes will bring confidence. If they don’t operate properly, the amp goes into a “runaway” mode and overheats to the point of destruction. (Sorry for thr long winded answer)

I had an SA-800 (silver face). Never touch the heatsink temp diodes 😳✌🏻