Law of averages says that there'll be a few hundred who don't turn up due to illness, family emergency etc., but people aren't going to buy a ticket for 1 specific game if they're not going to actually use it. I reckon 23.5k.
Just looked. All sections except East and West lower end blocks have sold well over 50% - the middle sections of all 3 home stands are almost sold out. I'd estimate that about 65% of available tickets have gone.