Bathroom door lock - where to buy?

Where can I buy a bathroom door lock like this? I went to Bunnings but they only have them integrated with the door handle. I want one that is separate.

 

Locksmiths will carry a range of budget and not so budget alternatives. That form of snib (thats its name) may or may not comply with the building code and looks quite unconventional esp as it just appears to be pushbutton. (external emergency release is required!, usually a pin / hole on the exterior)

Whats not showing is the latching mechanism inside the door. If its a non-conventional latch it could be problematic. Here is a link to some images which show the latching variations which may affect the door itself to avoid replacing the door.

bathroom privacy lock - Google Search

 

You might be able to use one like this Rectangular Sliding Cavity Set Privacy

 

Thats a very common one common to Lane, Gainsborough and others and available at Bunnings etc in different finishes. However the sliding door needs a precisely cut rebated cutout (comes with a template) and the size of the cutout needs to mask and not intrude beyond the former circular hole. Might work depending on latch setback in present door. The strike on the jamb may also be impacted as the other uses a different plate type. Hopefully its larger. Chisel so plate is surface flush.

(Long ago I worked for Black & Decker who owned Lane Hardware)