Step 1: find a good 88x31 button source, see below.
Step 2: download Chrome, Edge or any other browser that supports the Chrome Web Store.
Step 3: download plugin a image finder plug-in.
Step 4: let plugin analyse the page.
Step 5: select which images to download.
Step 6: drag the downloaded images to right folder.
Great resources to use:
The 88x31 GIF Collection
Yesterweb 88x31 Buttons
A.N. Lucas 88x31 button collection
NeoNaut 88x31
The Largest 88x31 collection
Exo.pet collection
YooHoo NeoCities button collection
Good old Google ofcourse