Games Workshop has never made either of them, and probably never will unless they do another Krieg supplement (which is unlikely). There is however a hell of a lot of scratch builds of Ragnaroks chucking about (and one or two Siegfriegs) on the internet. This guy has a
lot of them plus they're probably the best ones out there if your looking to build a couple too (plus he even made a walker variant if your into that kind of thing too).
http://z11.invisionfree.com/Work_In_Progress/index.php?showtopic=15801&hl=
Oh and scale wise Ragnarok's are about on par with a Macharius, slighlty larger give or take, and Siegefriegs are about the same size as Centaurs. Count a Ragnarok as a...Ragnarok or Leman Russ' in smaller games and the Siegfrieg as either a Sentinel or Centaur.^^
Oh and on the subject of canon they're both still valid if it ever comes up. ...Though why the hell would they be removed? ¬¬