The 10.x.x.x IP range is considered a "private" IP range, so no one technically "purchased" the 204 and 205 ranges you are speaking of. But if you are using 255.255.255.0 as your subnet mask, then the 204 and 205 ranges are on different subnets.
If you changed the subnet mask to 255.255.254.0, then your IP range would expand from 254 to 510, and the 204 and 205 ranges would be on the same subnet.
You can use an online subnet calculator, such as the one from http://www.subnet-calculator.com/subnet.php?net_class=A to calculate additional subnet/host combinations. (If you are using 10.x.x.x, that is a "class A" range, with 172.15/16.x.x as class B, and 192.168.x.x as class C - all of these ranges are "private").
If you changed the subnet mask to 255.255.254.0, then your IP range would expand from 254 to 510, and the 204 and 205 ranges would be on the same subnet.
You can use an online subnet calculator, such as the one from http://www.subnet-calculator.com/subnet.php?net_class=A to calculate additional subnet/host combinations. (If you are using 10.x.x.x, that is a "class A" range, with 172.15/16.x.x as class B, and 192.168.x.x as class C - all of these ranges are "private").