There are suppliers for luxury/spa brand shampoos in travel size bulk. I'd say YMMV for getting the same formulation as retail bottles, though, as the hotel version deals with more water conditions and less hair varieties. It also makes sense to cut costs here as most people won't compare the ingredient labels or detect the difference between higher concentration of inexpensive detergents and better formulations with higher quality ingredients based on a few nights.
Waterless formulations like shampoo bars and sheets are much easier to pack and lighter. They're usually SLS based.
Have you been using hotel supplied shampoo and conditioner? If you're able to switch between high end brands at home and hotel brands, your hair & scalp might not be that picky which makes finding a replacement so much easier. My scalp is sensitive to several detergents including harsher SLS (which is generally cheap and effective for cleansing) and using hotel shampoo for a longer trip would not be pretty. I mentioned the Neutrogena/Pantene's flatter bottles as they're easier to pack and you might want to find refillable bottles in a similar form factor or grab a few & refill with your desired shampoo. I don't use the contents of such bottles on my hair but it does the trick for hand wash laundry or washing the tub.