Mission nearly impossible
Here is how the whois databases work:
The RIPE, AfriNIC, APNIC, ARIN, LACNIC databases keep information about the address of the company to whose Autonomous System (AS) got the IP address block. These IP blocks are relatively large (several C classes (n*256 IP addresses - including network and broadcast address), or B class (64000 IP addresses - including network and broadcast address) or at times even larger.
Then, it is left to the responsibility of the administrator of the block to further break down the blocks into user-assigned subnets and report these subnets to the registry. Actually, this is mandatory, since by this process the registry knows that the AS is actually making use of the assigned IP block.
However, there is ABSOLUTELY NO VERIFICATION of the information placed within the sublock assignment. So it is very frequent that the address part will remain the same for a lot of subnets, or they will be assigned to the address of the head office of a large customer.
At the same time, there can be several AS operating in the same geographic region (for instance, several ISP's). So, the above described problem will multiply.

Your hypothetical tool will have to get the name of the location, query the whois databases until it discovers all subnets that are reported as operating in that location, and then present result that this location can PROBABLY have an IP address from the following blocks.