I'm struggling to think of many decent sites. There's Rimrose Valley. That's a big area, but currently a country park. I imagine if it was there, the proposed but highly opposed road through it might also get railroaded through. That would not be popular at all.
I see Brooms Cross, Thornton (but still L23) has been mentioned. Plenty of land, but isn't it farmland at the moment? I can't think of anywhere else in Crosby itself.
Then it's all farmland from Thornton on out towards Sefton Village, Maghull, Little Crosby and Hightown.
It'll be a shame if they move. I first went to see them there when I was in primary school.