Its hard to say exactly as you need to give the dimensions between and across the solder pads.
Also hard to know how high the switch can sit and what actuates it.
With those sizes , then you can trawl though Farnells/RS/ Rapids many pages of switches to try and find a match.
A possiblity is one of these cheap little though hole switches you can buy from Maplins stores for a pound; you might be able to rework the pins to fit the pads.
They do several of them but with different button heights
http://www.maplin.co.uk/p/105b-tactile-switch-kr90x