Provident Bank runs this ad in the New York Times:
I think it should read "an SBA..."
Upon encountering the abbreviation "SBA", most people neither think nor say "Small Business Administation" so even that reachy argument would not prevail. The whole purpose of "an" is to make nice-nice phonetically. This is something the Bostonians do in spoken English when they substitute "er" for a word's concluding vowel if the next word begins with a vowel, as in "Rhonda charges $200." but "Rhonder always charges $200."
This matter was also with us yesterday when C requested a ruling regarding the use of "an" before words beginning with an "h". And there you have the long an short of it.