Just as an FYI, to expand on Tom's reply, I have found that I do not need to go to a
3rd party icon program -- as Excel's toolbar "Customize" option allows one to go to
the "Command" tab, select "Modify Selection", click on your target toolbar button,
and then select "Copy Button Image", which one can then paste directly onto a
spreadsheet tab and name. Which is a nice self-contained solution -- and also
guarantees that there will be no sizing or other compatibility issues. Thanks.

Larry Adams wrote:

... do I need to consider building my own icon images via some 3rd party icon
program? (And, if so, any suggestions?) (Or is there a good library of images
available from somewhere that might work?) Also,...

... would there be any way to embed these separately developed icon images
directly into the Excel template so as not to need to distribute icon files
along with the Excel app itself?