Please note that proper etiquette says to spell out almost everything in
wedding addressing. That means, no abbreviations for street,
boulevard, avenue, apartment, state names, etcetera. Wedding envelopes
are more formal than typical business letters. For wedding envelopes,
five digit zip codes are appropriate.
Zip Code Finder
Here's a link to the United States Postal Service Zip Code Finder.
If you put in the address, city and state, it will provide the zip code.
(Hint - it's also good for catching spelling errors of street names and city names.)