The Football League trust are auctioning off loads of signed items from various football league clubs on ebay, including a few Argyle bits. Doesn't seem to be attracting much interest so you may be able to pick up a bargain.
http://www.ebay.co.uk/sch/theflt/m.html?_nkw=&_armrs=1&_ipg=&_from=
http://www.ebay.co.uk/sch/theflt/m.html?_nkw=&_armrs=1&_ipg=&_from=