Why that relay is missing from your bike is becoming apparent. There isn't a suitable and inexpensive replacement. Maybe Hella doesn't make them anymore and BMW has the market.
There are some less costly, maybe. There is this and it seems to have the same catalog part number—categorized as a new used part, I think. :giggles motobinsuk has one, too.
Why are there so many cross reference compatibles for BMW-61311459676 listed here
this and none are 60A as Inge refers to in a previous response.
All those is rated 40A, the OEM relay is made by Hella and is rated 60A....Hella # 4RA 003 510 60.
I'm also wondering if there are more unserviceable parts in the ABS system (also a reason the relay could be missing).
My other issue is the over priced shipping if I order from the USA.
All I ask is a foam wrap and a bubble mailer as that will save costs to ship to Canada. Probably less than $10US.