OV9

I have bought a set of lights which have a drl function.

I can easily feed an ignition switches 12v signal to run them, however I would also like the drl function to turn off when the sidelights are turned on.

Is there an easy way to do it with standard off the shelf components?

I've used traditional 4pin accessory relays loads, but is there a way to reverse their function, or another version which is latched on until it sees 12v to break the circuit?

Yes you want an N/C relay rather than an N/O. (normally closed / normally open).

Probably easier to just buy a new car