Hi iaratul,
Welcome to the club!
We don't offer a set of complete flash cards. There is an online set (also available for iOS), but they are more about recognizing scenarios than memorizing all the rules. However, most people find that self-created flash cards are the most effective, because they focus your attention on what
you need to study. There is some good advice on studying in general and flash cards in particular in our GMAT Roadmap ("guide 0").
In any case, there are indeed a great number of rules and conventions to memorize, but the real trouble goes beyond that. Memorizing is not nearly enough! You have to be able to apply these ideas flexibly, and sometimes creatively, to answer GMAT questions effectively. So flash cards are great, but they should only take up a small portion of your study time. Most of your time should be spent reviewing your work to understand how to improve your problem solving process. Below I've linked to a recent post on this topic.
As for your troubles with study and retention, it's hard to say much about your specific case without knowing more, but here are a few ideas:
1) Keep your study sessions relatively short--no more than 2 hours at a time, or less if you find that you aren't holding on to the ideas from later in the session. Yes, the GMAT will put you to work for 4 hours, but you're not trying to
learn for those 4 hours, and anyway you can build up your endurance over time.
2) Harness the power of repetition. Do the same problems again and again, sometimes right away. For some problem types (say, Overlapping Sets), a big part of your success will come from quickly recognizing the problem type and getting set up without wasting a lot of time. Redoing the same problem can help you to see what that feels like. Similarly, reworking the same RC passage several times can help you to feel what it's like to have a strong grasp of the passage. Then you can work to recreate that experience under test conditions.
3) Harness the power of repetition (again). See what I did there? Okay, so I have another point about repetition. There is a lot of research to support the idea of repeating material in widening cycles. In other words, review a problem or concept right away, and then after a bit longer, and then a bit longer than that. So you might do a problem and rework it right away, then review the next day, and then come back to it after 3 days, 7 days, etc. to make sure the lesson is sticking.
4) Do the painful part first. If you have trouble focusing, start your study session with the hard stuff that needs the most attention. Then do what's easier or more fun for "dessert."
As for your "logic circuit," tell me more about this. What sort of problems are you having there?
I hope this helps. Here's my post on reviewing:
how-to-study-effectively-with-official-questions-171547.html