Thanks for reporting this @FChris! Yeah that link is now dead I've pinged RSA via the Twitter blackhole https://twitter.com/odeke_et/status/901538219501563908.
In fact even trying to visit https://www.rsa.com/rsalabs gives a 404.

/cc @agl @FiloSottile for some ideas/alternatives.

The new link seems to be:
https://www.emc.com/collateral/white-papers/h11300-pkcs-1v2-2-rsa-cryptography-standard-wp.pdf

You can find it under the Wikipedia entry https://en.wikipedia.org/wiki/PKCS_1

Thank you @ulikunitz. Yeah, I saw that too and thought it made sense since EMC acquired RSA.
@FChris or @ulikunitz please feel free to send a CL updating it.

Change https://golang.org/cl/59351 mentions this issue: crypto/rsa: fix URL for the PKCS #1 v2.2 document in pss.go

I provided https://golang.org/cl/59351. I guess it requires a reviewer.