See https://lists.wikimedia.org/pipermail/labs-l/2015-January/003239.html : //toolserver.org/tiles/hikebike/8/205/135.png should be redirected to http://a.tiles.wmflabs.org/hikebike/8/205/135.png
Actually, http://a.tiles.wmflabs.org/bw-mapnik/1/1/1.png exists too, so:
//toolserver.org/tiles/(.+)$ → http://a.tiles.wmflabs.org/$1
//(a|b|c).www.toolserver.org/tiles/(.+)$ → http://$1.tiles.wmflabs.org/$2
Also asked by users at https://www.mediawiki.org/w/index.php?title=Talk:Tool_Labs/Collection_of_issues_after_Toolserver_shutdown&diff=next&oldid=1256793
Cf. T85166 for many other (simpler) tools which used to be redirected.