Actually, polymer handguards are available from Czech and Canadian suppliers. (I assume the Canadian companies are selling Canadian made versions, but one of the websites makes it sound like their product is from the Slovak Republic.)
These firms sell polymer furniture in Canada. Wolverine Supplies wrote me back with a list of everything they can ship to the U.S., but I accidentally deleted it. Basically, stocks are O.K., magazines and actual gun parts, not so much. Some of the handguards sold in Canada include picatinny rails.
INFRATEK TACTICAL
http://www.vz58.net/WOLVERINE SUPPLIES
http://www.wolverinesupplies.com/default.asp/The company that assembles the rifles for CZ-USA is selling parts and accessories through Tennessee Guns International. They have the black Czech-made handguards seen on the Tactical version. The set runs about $35, but you do get the complete upper handguard assembly (cover, pin, etc.).
TENNESSEE GUNS
http://www.tnguns.com/shop/index.php?main_page=index&cPath=42&sort=20a&page=4To my mind, you have singled out the most attractive 922(r) package that will also let you use unmodified military mags. A U.S. made black pistol grip with the Czech black plastic guards and folder, but built on a U.S. receiver, has the necessary parts count. If you switched around like you mentioned, it would still come in well under $600 on a ORF build.
For anyone else interested, I should clarify. Our CZ-USA rifles use receivers made in Moravia and a U.S. made fire control group that is superior to the OOW parts (usual source for builders). They are the best receivers, at least on paper. Unfortunately, you cannot buy a separate Technik receiver. I think the CZ-USA rifles are well worth the money, especially since you can't build one just like it. However, it is easier to have the features you want on a vz-58 and comply with the BATF regs if you build one on a U.S. made receiver.
The OOW receiver is much more money, but probably the best of the U.S. ones. The Prexis receiver is pretty reasonable, but it is difficult to build, according to some. There is a fellow on gunco.net that is doing a build tutorial with pictures for the ORF receiver. I'll try to find it and link back to it here.