Paul Chen do a set of throwing spikes in an arm holster. They are available from www.Blades-uk.com
for £40 ($80) thats the only U.K. site i have seen them on (British law hates shuriken of any sort). If you are in more relaxed climes, i am sure you will find them listed on numerous sites.
Happy throwing [IMG]http://www.fightingarts.com/forums/ubb/smile.gif[/IMG]