Searched both by league number (35416) and name (Thundernuggets). Neither came up as available leagues, and it didn't show up in custom league browse.
Are you sure the league is set to available?
Okay, I don't know what's wrong, I think it's because I'm trying to use last year's league with new teams.
If you want in, just DM me your email address and I'll send out an invite.