They are and always have been "very rare". I was always into glass items so I have always looked for them in loot. In all the years I have hundreds of skill talis but I still only have a few glassblowing (maybe 15) and none of them are above a 26.
The same as Zeke above, our guild has always liked Melisande and Dreadhorn so we have looted a lot of talis but as above, just a few of the glassblowing ones.