Green’s Dictionary of Slang

walk-up fuck n.

[SE walk up + fuck n. (1); one needs only to walk up and ask]

(Aus.) a woman who is readily available for sex.

[UK]Partridge DSUE (8th edn) 1305/1: C.20.
[NZ]McGill Reed Dict. of N.Z. Sl. 226: walk-up/walk-up fuck Promiscuous woman — you walk up and ask her. ANZ C20.