I second what Blackca3 said, apply anyways despite their requirements. I must've applied to about 15 different practices for their open dental assistant positions, and most of them told me the same thing you're hearing now: "You need experience, x-ray certification, etc." It is extremely difficult to be a DA without any prior experience or connections. I eventually lucked out and was hired by a patient dentist willing to train someone with little to no experience. Keep applying.
That being said, you don't need a JOB as a dental assistant for dental schools. Volunteering at clinics and other dental related volunteer opportunities will be just as good. As for money, your Uber gig pays well.