I think you can, or you used to be able to.
About 5 years ago one of our club members ran a small business selling
Rootmaker pots and Myco spores. _I bought a packet at that time and used in in transplanting some trees I brought back from Japan.
The instructions were to work it into the top inch or so of soil on established trees. _You use a fair amount of this stuff, like a tablespoon. _It wasn't cheap.
Shortly thereafter, a bigger company, one that makes those hydrophyllic granules that you can use to make soil-less hydroponic soil that you sometimes see at the mall. _Looks like clear jell-o crumbled up.
Anyway they didn't mark that on the package, and so I didn't know and mixed some of the stuff into the bonsai and went on a little vacation with instructions for my parents on watering. _When I came back, all of the trees were covered with what looked like about 2" of ice chips. _
I was shocked and ran around collecting all this alien crud and filled a 3 gallon tub with it. _Since that time I haven't bought or used the stuff, and have just harvested some of the myco when I repot.
I found a _few links on the web for inoculants:
http://www.agroforester.com/agfor/mycorrhizae.html
http://www.hortsorb.com/Biological_Specification%20.htm
(This one has a reference to a polymer gel, which I believe is that nasty stuff I was talking about)
http://www.bio-organics.com/FAQs.html
http://www.mycorrhizae.com/slides.html
http://www.btinternet.com/~colinlew...ading/Myco.html