Navigate to zoneedit.com in the DNS lookup field enter foursquare.com and in the dropdown select "Ip Address (A)" you will find only one record listed. After further research I found that Foursquare is hosted at Amazon Web Services and the most likely scenario is that thy will have have multiple servers hosted behind a single IP'ed load balancer. You will need to get the IPs for foursquare.co.uk or any other top level domains it may operate under (COM,NET,CO.UK and so on) but from what I can find CO.UK is the only other country it operates in.
