I need help with sorting out the difference between 了, 著 and 到 when used as verb complements. I have learnt most of my Chinese in Taiwan and in my experience, Taiwanese people don't use 著 as a verb complement very often, except in some common phrases like 睡不著 and similar. I don't think I've ever heard anyone here say 買不著 or 見著. Most explanations I find online are next to useless, saying more or less the same thing, i.e. that these complements indicate the possibility of an action or if a result/goal has been attained.
I don't have much of a problem with 了 and 到, but I don't know how to use 著.
In order to have something to play with, here are some examples I found online for 著:
(1) 听说你想买一本汉英词典，**买着**了吗？ (2) 我去的时候，车已经开了，我没**见着**他们。 (3) 在那儿什么东西都**买得着**。 (4) 有些东西你带了也**用不着**。 (5) 我的药呢？刚才还在桌子上，怎么**找不着**了？ (6) 我经常**找不着**北。 (7) 这是十年前流行的衣服，现在已经**买不着**了。
睡著 is the only sentence where I would use 著 naturally without thinking too much about it. When should 著 be used? What's the difference between that and using 到 (or 了 in some cases)?
Drawing from the examples above, what's the difference between:
(3) 在那儿什么东西都**买得着** and 什麼東西都**買得到** (4) 有些东西你带了也**用不着** and **用不到** (5) 我的药呢？刚才还在桌子上，怎么**找不着**了？ and **找不到**了？ (7) 这是十年前流行的衣服，现在已经**买不着**了 and **買不到**了
In the above cases, I would always opt for the second version and they seem to mean pretty much the same thing to me. Please help!