Tablebases are commonly available from a variety of sources. Indeed, Convekta has a set of five man (including some six-man sets) available on CD and DVD. But getting a complete archive of 6-man tablebase on your own machine can be difficult. So far, Eugene Nalimov has generated over 600GB of tablebase files already, and Convekta expects twice that total will be generated before the set is complete. So getting 6-man tablebases on your own computer is a big problem. Luckily, Convekta has made these files available over the internet.
As far as I know, no other commercial entity has done this for the 6-man set. However, as of today, Convekta is making this data available through their new Russian playing zone: ChessPlanet.ru. Note that the zone is not fully functional yet and is not optimized for English speaking people. However, a wide variety of features are working already. You can access the tablebases through the playing zone as follows:
Download the ChessPlanet client and set it up: http://www.chessplanet.ru/program/chessplanet_e.exe.
In the future, you will be able to import EPD positions from clipboard (Shift-Ins will paste the position into the board). Try these for example:
8/pk6/8/8/8/8/N7/N6K w - -
8/1k6/8/8/8/8/N7/N6K w - -
You cannot mate with two knights and kings. But if your opponent has a pawn, checkmate is possible.