it's not just downloading them, here what we hate about using .3DS files from other sites
1- because most of them are not in small size, they needed to be uploaded in reliable host, that's mean people will put ads in order to download from the link and sometimes one link is going to be brook.
2- you can't use a .3DS files converted from .cia, you have to use .3DS files dumped from legit card so you can use them on OFW, it's not like GW which you can use converted .3DS games very easily.
3- you have to use a $80 cart in order to play 3DS games? why you would spend $80 to do that? unless you have $80 to burn and you want all your 3DS games inside 1 cart, but that also will bring to the next big issue.
4- and this is very important, you have for example 30 games on the cart, in order to reach game no 15, you have to press 15 times, those button is fragile and can be break in time, so it's not reliable way to switch games.