Homemade Truffle Salt
The process is apparently very simple: grate fresh truffle into salt using a microplane, and pulse with a food processor to blend.  One source said the flavor intensified over time. I can't find a ratio either, but it looks like about 10:1 salt:truffle, maybe less.  

Flavor is always going to vary a bit with something natural such as truffles, but if your result tastes nothing like store truffle salt, there's a couple possible reasons.  Perhaps the truffles you're using aren't truly fresh.  I suspect the store truffle salt adds flavor extracts or synthetic truffle oil to punch up the flavor a bit. Stuff derived from real truffles is often milder but more complex than things using synthetic imitations. 

Finally, you might try using a different salt.  I'd suggest the best sea salt you can get your hands on. Rougher salt grains might absorb flavor oils better than more regular ones, and better sea salts add their own subtle tastes.