Exposing postal code as a Views argument

I have a scenario where I want a block on my page to reference the location details of the main content area. In other words, lets say the content in the main body of my page has location information of 123 Smith Street - Houston TX 77002, I want my block on the page to reference other nodes that are in proximity to that postal code (77002).

Unfortunately, in all the Views I've tried, I cant seem to find the Location: Postal Code field - I've created node and location type views, and both are limted to:

Location: City
The city of the selected location.

Location: Country
The country of the selected location.

Location: Phone
Error: missing help

Location: Province
The province of the selected location.

Anyone have an idea as to how I can get at that data? In the interim, I've set the arguments to City and Provice, so my block will look for Houston/TX as values, and generate the desired result. But it would be much more efficient if I could get at that postal code value.

thanks...