I have found the best place to look is in my own mind. Figure out what you are looking for in a layout. look at some MRR magazines for Ideas. Find some MRRs in your area and see what they have. Go to train shows they usually have at least one layout operating. See what others are doing. Make a drawing. Look it over see what you like ad don't .Make appropriate changes oh yeah try to find a local club, go talk to them, pic their brains . Build what you think you want not with a lot of detail and scenery. run it for a while (3-6 months) now take it apart start over with new layout. Make the changes you think you want do a little scenery. give it a little time and do it again from scratch. Remove scenery starting with bare plywood. You might note I have been saying "what you think you want" . That is because you probably don't really know. Doing it this way you learn what not to do and what you want in a layout. To many people jump into it with both feet, end up with a huge layout spending a lot of money and are disappointed with result because they didn't know what they actually want. When you figure out what you want in a layout build it. Hope this helps.
I've found that looking Web Search Engines, and entering the Size scale and Train Layout, will give you an array of sites to look at.
Trainsetsonly is a good site.
I've used what I have found and have formed my own design.