Question about tire size for 14"X 7" Mopar Rallye Wheels

According to this tire calculator that I like to use, 255s are the biggest tire recommended for a 7" rim. That being said, I do not know how hard/easy it is to find 255s if they are even made & they will only give you 0.4" more width & 0.5" more height.
http://www.rimsntires.com/rt_specs.jsp