PayPal is the only option for the JimdoPro subscription right now. Stripe is available for JimdoBusiness, so you could upgrade for it, however, JimdoBusiness is $240 per year as opposed to $90 per year for JimdoPro.
There isn't a way to integrate Square directly with Jimdo, however, the link that I sent you was about using the products that you've added to Square Market to a website. So, what you could do is add the tickets to Square Market and people could check out with Square. This basically circumvents the Jimdo store features, but that shouldn't be a problem because it sounds like you're used to Square anyway.
Here's a video showing what I mean (I used a necklace as the store item because it's the only Square embed code I have, but you would use the embed code for the ticket): http://www.screencast.com/t/UZfMTGm8c7KP
Hope that makes sense. Let me know if you have any follow-up questions!