The most popular commercial sets at present seem to be Osprey's
Ronin and
Daishō by the Ministry of Gentlemanly Warfare. Though the latter is subtitled 'Skirmish Wargaming in Mystical Japan' it is perfectly well suited to purely historical games. There are also free sets available online, including a couple here of varying complexity and detail:
http://www.jimwallman.org.uk/wargame/I see someone beat me to it. I nearly mentioned
Torii, but haven't actually seen it, though I have the same publisher's
Kensei. Both of these, however, also have a 'mystical' slant, and appropriate models may not be easy to find in 1/72. As with
Daishō, however, I am sure this is easy to ignore, at least initially.