spoofing an ip is tricking something into believing your traffic came from a different source.... you dont need to own that source or even be able to connect to that source to spoof its ip as its something you do on your own machine
if you want to buy a server and use its ip any server will work you don't need to "spoof" it
you can just redirect the connections in or out or both to your own computer with a number of methods such as,
a reverse proxy or vpn static routing or masquerade via iptables tunnelling protocols and many other applications software or hardware designed in a similar manner
you dont need to look for this you just need to install or purchase it from a service that will install something of these sorts for you.
using the proper terminology you will find things easier ... dropping words like "spoof" might help too as you say that to anyone and they will suspect you of something illicit
some references
reverse proxie



vpn
IPsec - Wikipedia, the free encyclopedia
Point-to-Point Tunneling Protocol - Wikipedia, the free encyclopediaLayer 2 Tunneling Protocol - Wikipedia, the free encyclopedia
iptables
http://en.wikipedia.org/wiki/Static_routing
and so many others
keep in mind you will have usage limitations and terms of service to contend with depending on what you intend on doing with it or who you get it from