Where to buy Internet IP addresses

Optimum Online business only offer 5 static IP address. Where can I buy a block of Internet IP address for Business? How much does it cost? Most of our devices only require an internal IP address to reach the internet, but we have a Juniper DX for load balancing. We must provide Juniper DX with an internet IP address and point it to internal IP address for customers to be able to reach it from the internet. this is for testing and development purposes and will expect several servers on Load-balancer. The 5 static IP addresses just won't be enough. Thanks in advance Louis