In tips you can find this:
There are several irregular plural forms, usually these include changing the main vowel.
en man → män en mus → möss en hand → händer en bok → böcker
BUT i googled irregural pluras and find this: http://www.cram.com/flashcards/swedish-noun-plurals-irregular-1499156
Why here in tips are not all irregular plurals?
Also what about pasta? Pasta is en-word ending with -a. Why is not pastor? Is pasta some exception and if it is where can I find other if there are any?
I don’t know of that rule, but you can just make any word a two-syllable word by making it a compound, such as making hund into kamphund. It would still have -ar, also -ar is the standard ending for two-syllable words on -e like pojke and gubbe. I can also think of words like cykel or fågel or syster that also have -ar.
But I understand your point that tallrik has no –e, –el or –er, nor is a compound word. It could be that it sounds like a compound word to Swedish speaker even though it isn’t. It might as well be a compound word such as tall+rik just as kamp+hund is one because they have the exact same melody, so then it would make sense that they are treated the same way.
I don’t know though.