Alpha makes a big deal out of their product support. That doesn't sound like first class customer support.
Part is clearly listed, priced at $9 with photo on Replacement Parts listing for this 76A amplifier.
Very few people at Alpha today were working at Canon City, CO
when Dick Einhorn (ETO) was making this specific amplifier in 1970s and early 1980s.
When I was restoring my former Elmer K9EWJ(sk) Alpha 76PA amplifier in 2005, I stopped by Alpha in Colorado, a few days after its sale/separation from the bankruptcy of Crosslink.
I walked through 76A series spare parts shelves at that time, picking up odd parts I needed (minor, like the colored lamp boots behind meters) for repair/restoration.
At that time, I asked about those circa 1970s front panel switches. (Mine were OK).
The switch assembly itself is available, BUT the button itself (colored flag change) was discontinued by switch mfg.
I forgot the specific mfg. -- but Alpha had information.
As I remember, a plain button (no flag) was available from mfg. at that time, but Alpha was not stocking.
I referred another restorer to Alpha for the switch about 2 years ago.
he acquired through an eBay auction, and its switch assembly was burnt up, but buttons OK.
The SWITCH is LISTED on their web page (NOT front button), under Replacement Parts Internal switch mechanism for the push buttons on the Alpha 76A, 78, 374A series of amplifiers. $ 9.00http://www.rfconcepts.com/Alpha-76-PA-C-PC?range=11%2C20%2C100
Switchcraft made a button assembly that was similar (used by Harris/Gates for broadcast & military)http://www.switchcraft.com/productsummary.aspx?Parent=490