Zamioculcas zamiifolia
trade

Availability

Although the species had been described for the first time more than 170 years ago and has been offered by some speciality nurseries for decades as an aroid curiosity, it was made available to a significantly wider public only about five years ago (around 1996) by dutch nurseries (see below). It is still quite rare in flower shops (more abundant in gardening discount stores), and a bit expensive (probably due to the fact that it's growing quite slowly). Here in Austria, a (nearly) mature plant presently costs some 15-25 US$/€ (~200-400 ATS) in retail trade (younger plants sometimes only around 10 $), compared to about 40-50 $ that were charged for the first Zz specimens that I have seen in 1997.
I assume that most of them are propagated vegetatively, as this is the fastest and easiest way.

Sale figures from Dutch flower auctions, according to Bloemenbureau Holland [source article no longer available], or as quoted in this article by Geert Devriese, 2001. The title means "Continued increase in demand for Zamioculcas":

Where to buy
Zamioculcas
(draft)

: The following compilation of some online nurseries is for your conveniance only. It neither claims to be complete, nor do I have any influence on actual availability of plants or other goods or services offered, nor am I party to or do I profit from any business or payment deals with any of the linked companies. Buy or order at your own risk. For certain species, genera or families of plants, CITES restrictions may apply (Zamioculcas is not listed in CITES). A phytosanitary certificate, an import permit or other documents may be required for importing plants to your country. Check with your authorities before ordering anything. I do not take any liabilities whatsoever.

www.tropiflora.com
wide assortment of bromeliads, orchids, aroids,
succulents and other greenhouse plants;
well done illustrated information section.
Online orders.
Sarasota, Florida, USA

The Philodendron Phreaque
lots of Aroids and several other interesting stuff;
(some in limited supply only). Many photos.
Both forms of Zamioculcas. Online orders.
Davie, Florida, USA

www.glasshouseworks.com
offers the "smaller form of Zamioculcas".
Online orders.
Stewart, Ohio, USA

www.rareflora.com
succulents, caudiciforms, ferns, bromeliads...
Online orders.
Delray Beach, Florida, USA

Plant Ranch
wholesale and direct selling. No online orders.
Arvada, Colorado, USA

Sunshine Tropical Foliage
wholesale plants to the trade in 48 states,
Canada, Europe and the Caribbean.
Homestead, Florida, USA

Initially, I've planned to make a larger list of nurseries, but I've found that there's so many, that I think it's easier if you just try searching the web (e.g. for "Zamioculcas +[your place or country]"), or check some gardening discount stores in your area.

In Austria, you can find Zz occasionally e.g. at Baumax/MegaBaumax outlets (with garden center), at Bellaflora or at Holland Blumen Mark.