No there is not. Either get it repaired, but good luck in finding someone to do it, but there are some who will, otherwise the gas tank needs to be replaced.
I would absolutely just replace it, not worth the hassle or expense trying to repair it. Most leaks are from rust and you do not want a rusty gunked up tank unless you enjoy replacing fuel filters and pumps.
If it is a pin hole rub a bar of soap into the leak.
Looking for a Used 300 in your area?
CarGurus has 1,051 nationwide 300 listings starting at $2,300.
Search Chrysler 300 Questions
Chrysler 300 Experts
Related Models For Sale
Used Cars For Sale