The V3 Ultra Catsuit has been removed from the DAZ store.

I don't know why they do that.  It doesn't even save them server space.  If you bought it before and it's in your order history, you can reset your order and re-download it.  So it's obviously still there.

I guess they just want to de-clutter their store.

I am still very fond of the generation 3 figures.  Partly because I have the most stuff for them.  I also think they were more...separate.  Unique.  V3, Aiko, the Girl, all have very different styles.  The generation 4 versions are more alike in style. 

I have a feeling that they may release the catsuit again in the future, perhaps as a freebie for joining the PC or something. 

Otherwise, the only thing I can suggest is begging DAZ to let you buy it.  They've been pretty accommodating to their customers lately.  And hey, it shouldn't be that hard to convince them to let you give them money, should it?