WARNING ! ! ! WARNING ! ! ! WARNING ! ! !
I did some searching to various sites I order some of the special needs stuff for my classroom. And then I did a search in my Search Engine. I found the same thing you did. This is actually a significant concern to me. I looked at sites from England, Canada, and here in the US. All of them were listing the product as on Backorder. Some of them look like they have been on backorder status for six months. To me this looks like the product has either been discontinued or the company is working on a new version. Many of the sites are even starting to have the accessories on Backorder. I will caution you about buying this product if the future of the product is in question.
There are many other Special Needs strollers out there. Yes, many of them have price ranges above $1,000 but some have a price at $500 or under. I know the Maclaren Major Special Needs stroller is highly praised by parents of children with special needs, but that is partly because it has been around for a long time. If I recall correctly, Maclaren had a Special Needs stroller back when there was little else out there for older kids.
Currently you have brands like Convaid, Special Tomato, Baby Jogger, and a variety of lesser known names that are making Special needs Strollers. Finding the right thing for your daughter and your families needs is not necessarily something you want to do at the last minute as you are trying to pull off a Disney trip in what 13 days.
I recommend that you take a deep breath, a step back, and face some reality. 13 days before you leave is not a good time to try and find a multi-hundred dollar product designed to last you and your daughter several years. You can not just go into a store and try one out before buying it when it comes to these strollers like you can with baby strollers.
I recommend that you go to Orlando
Stroller Rentals (if you still can) and rent the Special Needs stroller they have. It will take the stress off the trip, it will give you time to find a stroller that works for your family without feeling pressured to get what is in stock, and it will allow you and your daughter to find out if a stroller is what you really want at home for you 9 year old daughter. If you are only going to use it on vacation, then renting is the best way to go. You daughter may be fine in a stroller at Disney but after the trip when asked if she wants one for a trip to the mall, she may have a very different feeling about the issue. But she will not have an idea about this till she experiences a stroller at her current age. Just rent one for this trip and then look at the purchase concept when you get back. I know the $120 rental price is steep for week rental, but I suspect it will make the trip a lot less stressful for you and your DD.