There are three Walker name tartans, all designed in 1993 by Robert Walker Hawks of TN. There is a red one, named "formal" or "evening" by the designer, a green hunting one, and a white dress one. Any of these three would require custom weaving for you, but they can be had.

Other than that, the Walkers are traditionally considered as septs of Clan Gregor and the Stewarts of Appin, so those tartans would also be possibilities.