Generally Blyxa's are "bad travellers" - they respond fast and bad, to being send around, usually arriving in quite poor condition (they recover really fast, though, given proper conditions in aquarium) .
This make commercial distribution difficult. Tissue culture is the way to go.... and Tropica is working on it (quality still not perfect, admittedly!)
Blyxa japonica is easier to grow successfully (has lower demands) than is Blyxa aubertii. Blyxa japonica is also the smaller species. This is making Blyxa japonica more common in private aquaria and easier to get hold on.
I agree, though, that Blyxa aubertii is a truly gorgeous plant, deserving more interest.....keep searching and good luck.