Tiger salamanders are known for being incredibly difficult to breed in captivity, so it's very unlikely that you'll find anyone selling or giving away eggs. Since tiger salamanders (ambystoma tigrinum and ambystoma mavortium) are listed as Least Concern in most states you're fine to collect a few eggs from the wild, which is what I have done. It's a bit late in the year to find eggs though since they breed in early spring (February through April).