A modern large chess variant (with close resemblance to some older variants, like Capablanca's Chess, is the game Janus Chess. Several chess masters and grandmasters play this game, and have participated in Janus Chess tournaments, including Korchnoi.
A booklet on Janus Chess is sold by Stephan Blasius, Lebacher Str. 30, 66606 St. Wendel, Germany, for DM 8, plus an extra amount for postage (Variant Chess mentions DM 3 for postage). Janus Chess sets are sold for over DM 100 by Schachhaus Madler, Wagenerstr. 5, D-01309 Dresden, Germany.
The extra pieces of this game, the Januses, look like knights with some extra `pin' put on their head, making them look a little like unicorns. Actually, from the picture in the brochure of Schachhaus Madler, it looks like these Januses are actually made by adding a little wooden horn or pin to a normal knight (but I can be wrong.) In any case, this may be a cheap way of making a Janus chess set yourself, when you have an extra cheap or old chess set of which you do not mind to modify the knights.
The game is played on a 10 by 8 board. Each player has, in addition to a normal set of chesspieces, two Januses and two extra pawns.
The opening setup is as follows:
King e1; Queen f1; Janus b1, i1; Rook a1, j1; Knight c1, h1; Bishop d1, g1; Pawn a2, b2, c2, d2, e2, f2, g2, h2, i2, j2.
King e8; Queen f8; Janus b8, i8; Rook a8, j8; Knight c8, h8; Bishop d8, g8; Pawn a7, b7, c7, d7, e7, f7, g7, h7, i7, j7.
Note that the Januses go between the rooks and knights in the opening setup, and that the king is at the left of the queen, so the queen still starts at a square of her own color.
A Janus has the combined moves of a bishop and a knight. When a player castles, his king goes to the square on the b or i-line, i.e., when a player castles short, his king moves three squares, and when he castles long, his king moves four squares. All other rules are as in normal chess.
Issues 18 and 20 of Variant Chess.