Consider camping and hunting gear. In fact, consider anything that's outdoor related. Campers, hunters, sportspersons, and athletes often have the same issues we have. We're all exposed to the elements and we all enjoy a bit of comfort.
So, some ideas......
Underwear - a subject very few of us broach, but you'll find it's a highly discussed topic among long-distance riders. In general, it should be supportive but not too tight. Ideally it will have no seams you have to sit on. For comfort, it should wick moisture away from your skin quickly. Cold weather or hot, your underwear is the foundation of your layered clothing package.
- Some types of baseball shorts are lycra based, highly supportive, and come with hip pads sewn into them. They're relatively inexpensive and are available at most sporting goods stores in the spring and summer.
- Silk, lycra, or merino wool longjohns are options that should be considered for every rider in every environment. UnderArmour makes "Heat Gear" designed to keep athletes cooler and these can be worn underneath full race suits to considerable advantage. Merino wool longjohns help keep a rider warmer without bunching up in the middle like a two-piece.
Rain suits and rain gear - These don't have to be motorcycle specific, but in all honesty, it helps. I can't think of another sport where the rain comes at you with such speed and always from a singular direction. Alternatives will work in the short-term, but a moto-specific suit will generally be better suited for our application.
Ski gear, such as balaclavas and neck protectors - These are generally grafted into service for motorcycles. I'm not aware of a single company that sells its head and neck products exclusively to the motorcycle market.
Gloves, boots, leathers, and helmets - This is a tender subject because these things are pretty exclusive to our sport. Is there another sport where you might possibly put your body on the pavement at 100 miles an hour? In any case, this kind of gear is expensive. On the other hand, this kind of gear is a super bargain when compared to skin grafting or death. Do the research and buy what you want. There are way too many options and possibilities for me to discuss them here. If you can't afford basic protective gear, you can't afford motorcycling.