Just input model railway (or railroad) track plans into Google and you should bring up loads.
A few will be Scarm type plans and there's a bit of pinterest click bait, then you can always refine your search a bit more. For example prefix with "Large American" or "HO Scale" to filter the results.
Be aware though the big companies like Kalmbach and Peco rigorously protect their copyright and you will find few of their plans around the net. You could of course support your local model retailer and buy a couple of plan books which you can then scan for your own personal use and library.