Honestly, I see just as many longhairs as I do smooth. It's hard to find a reputable breeder period, if you're looking for a Dachshund. No matter whether they're long, wire or smooth. I'd also say that whether they're longhaired or not, 99% of the ones I see are either black and tan or red. I've met one blue/tan, one fawn/tan, a couple of dapples, one brindle and about five piebalds.

Longhairs most certainly are not rare, and blk/tan is the second most common colour in the Dachshund. That lady obviously doesn't have a clue what she's talking about. The breed as a whole is also extremely popular. I run into them absolutely everywhere and I also own two (one red, one blk/tan - both smooths).