I think the thing is that for example 6 PhDs are offered but there is only funding for 4.
The best candidtes for 6 will be accepted then the department will choose the best project or student for the 4, the other 2 PhDs don't get funded and are essentially not available at all (probably until the next year)- as far as I'm aware,
So you would either get it with funding, or not at all - I don't think any of them would expect you to find funding - therefore you don't really need to state that you require funding to accept the post - but you can still discuss the funding with them
Good luck
S