Try Elland Road, just around the corner. They have played there before 54,000 against Leeds as I recall and in Division two.
Sadly Hunslet can no longer be considered Leeds' "local rivals". Two generations have grown up with Hunslet being the poor relation and with no matches against each other. No longer is there a real rivalry between North and South of the river.
I suspect kids from Hunslet, Belle Isle, Middleton and Beeston gravitate towards Headingley nowadays. Hunslet being in SL would hardly change that imbalance.
If such a match were to draw a 20,000 crowd, then 18,000 would be Leeds fans. As sad as it may be Keighley, today Leeds fans consider Bradford as the big grudge match.