I had visited the websites of several German museums, and though there are several museums which seem to have decent collections of historic clothing and folk costume, none of them have complete or even partial online collections. It seems that if I really want to study Tracht in-depth, I will have to go to Germany.
In no particular order, I would love to visit:
First- the Germanische Nationalmuseum in Nürnberg.
Photo of part of the Germanische Nationalmuseum's costume collection.
Also- the Bayerisches Nationalmuseum in München.
And- the Modemuseum at Schloss Ludwigsburg.
All three museums are within a less than two hour train ride of each other, which would actually make a research trip quite feasible within a fairly short trip. I first need to email the museums though to see if it would be possible to look at objects in their collections not on display, and then see if I have the funds for such a venture. It might really be worth it to go, as there's really not much by way of German tradional clothing in museums here in the UK.