Unfortunately, your humble correspondent hasn't discovered the secret handshake to get the relay's UK producer to ship me any. I contacted the company that spiderserie4 had found that produced a LED enabled relay that looks spot on for S3/S4 spiders. If it worked as advertised in would be a good deal too, as minus VAT, it would run about 16-17USD (before shipment cost).
But Simtek only ships direct from a web order within the UK. Outside of it, you have to request a purchase quote, which I did. I also asked it the relay was a replacement for the 4-pin units in later series Alfa Spiders -- and that's where things are hung up. They won't ship until they can verify it's a match (input/outputs). We're in a cycle where I ping them every 3-4 days, and they respond quickly apologizing and letting me know they'll get to it in 1-2 days. But the cycle continues. Probably a one-off order to the U.S. isn't ringing any sales bells (I did note to them if it works there would likely be other interested parties). I also offered to just take the risk and plug one in if they'd send it to me, and if the car burst into flames, that would be my problem -- but still no dice.
Anyway, at this point abeasley has offered to request purchase quote for a couple of units w/o mentioning the word 'alfa' (the relay was used by multiple euro car brands back in the day, but I don't know what brands Simtek considers 'tested'). The other option could be if there is any UK-living, Alfa-loving members reading this string and want to help, let me know. An internal UK order looks relatively simple.
So that a long response to a quick bump of curiosity. Now, it's out to de-weed the yard.