Hi, Thinzar, welcome to the forum! 
You’re not alone in your disappointment. I don’t know when IS/A and B will be restocked. You’d have to ask John Sebastian about that. Women don’t have much to choose from anymore. Don’t ask me why. It’s been asked about countless times and I just don’t have it in me to reiterate it all. Search around the forums.
Anyway, we can only work with what’s in the store and right now TAH and TAL are in stock. Previous formulations of IS/A have been TAL based and IS/B was TAH based. They also contained other pheromones although we can only speculate as to which ones because exact formulas are not revealed. So, if you want to get an idea of what the Instant Sexy’s were like, you might want to try both of these molecules while you can. They were just restocked a few weeks ago after being OOS forever. So get 'em now. No telling when they will disappear again.
Yes, you certainly can layer TAH and IO. It’s a nice combo. But I would recommend trying them one at a time, first, and finding your sweet spot for each. That’s the number of sprays that are effective to provoke a reaction in your targets. Once you determine that, you’ll be better able to layer molecules for the best effect. Taking the time to figure out how much you really need also helps prevent wasting product. Especially in light of how much the cost of these products has increased. Why over spray if you can get the results you’re looking for with less product! 
If you’d like to receive a $25.00 Gift Certificate towards your purchase, go to the Intro section and formally introduce yourself.
Make sure to read the stickies at the top of each forum. They’re there to help you help yourself along in discovering the wonderful world of pheromones and will get you started off on the right foot. You’ll find answers to alot of newbie questions right there. With a little time/patience/experimentation comes an understanding of how this works and before you know it you’ll be using pheromones to your advantage.
Good luck and have fun!
Bella