As the previous respondant noted, the Post Office 
is cutting back on their IPMO services, making it 
less available than it used to be.  Many small, 
non-hub Post Office branches are not re-ordering 
the forms when they go out of stock, thereby 
getting out of the business.

Call ahead to the PO that you want to go to, to 
make sure that they have IPMOs available.  If 
they don't, they can tell you the closest PO that 
is still in that business.