Is a public school PTA (parent teach association) fundraiser purchase tax-deductible? if so, where?

Yes, it's deductible as a charitable contribution either on Schedule A as an itemized deduction, or if you don't itemize you can deduct up to $300 on your Form 1040.  To do so in TurboTax, just click on Search, type on "Charitable Donation" and then select "Jump to charitable donation".

The difference between the amount you contributed and the value of the  item received is deductible if the PTA is a registered non-profit. It probably isn't and you probably didn't pay much more in the fundraiser than what you received, so this is probably not worth pursuing.
If you did pursue it, it would be deductible either on Schedule A, or if you have no other tax-deductible contributions to registered non-profits, as part of the $600 cash contribution that can be deducted even if you don't itemize on Schedule A.

All the same, good on you for participating in this fundraiser! It sounds like a worthy cause 🙂

[The amount is $600 for couples filing jointly, $300 for each single taxpayer.]

Did you receive an item in exchange for this?  Donors who purchase items at a charity auction may claim a charitable contribution deduction only for the excess of the purchase price paid over its fair market value.