Resource For Historic USPS International Postage Rates?

Are there any offline or offline references to look up what USPS international postage rates were in effect at a particular point in time, including rates by destination, class, weight, letter vs. postcard, etc.?

I have found a few resources for historic DOMESTIC letter rates, but nothing on international rates.

Specifically, I'm wanting to know what the rates were for letters sent to foreign destinations in 1898.

Thanks.

I would start with this companion volume to their excellent domestic rate book:

Google "United States Official Postal Guide, United States, Post Office Dept. January 1, 1900." I didn't find a copy from 1898.