Smitty - Is your booster club a 501c3 organization? If not, there's no way to obtain that # without that IRS certification. If you are a separate entity than the school you may not be able to use the school's 501c3 number bc it's their # and they can, potentially, lose their 501c3 designation letting you use their # (regardless that you are using it in good faith) - so I'd suggest avoiding going that route. If the school PTA has their own # they can solicit donations on their own. Perhaps local children's sports clubs (football, softball, soccer, etc. might donation the registration $ for one season - thought that typically only works if you have a limited # of schools in your district otherwise they'd be giving it out).
Like Mc Kenna mentioned, most local businesses will be fine w/o the number and won't ask for it (car washes, salons, restaurants, etc.). Try local music stores who give lessons, a local golf course &/or golf pro, local skating rinks and bowling alleys, Zumba or yoga classes, kayak rentals, local ski resort, etc, etc. etc. ,) Larger, more national chains often require that 501c3 # (and check to verify your organization's status) and not the state tax exempt form. Some actually also require a copy of the actual IRS letter confirming that an organization has the 501c3 status (I have to submit this to a few companies annually as part of my donation request). Good luck