The standard has always been Levine's Guide To Knives and Their Values. Unfortunately, the latest edition was not done by Mr. Levine. The wide perception in the community is that the values given in the new edition are off quite a bit in many cases. The last edition editted by Mr. Levine is to old to be very accurate any more
The other big problem is that collectibles across the board are in the proverbial toilet along with the rest of the economy. So, the guides in just about any field, coins, art of all kinds, cars, sports trinkets, stocks and bonds, whatever you might collect, are all pretty much wrong these days.