I don't think anyone makes a quality loading tap anymore, I imagine theres a chinese thing out there with a loading tap, but i think i read somewhere that they were quite tricky to keep a good seal.
You might find that the loading port on a HW97k would be easier to load, as it isn't just cut out on one side, it goes all the way over the top, to cater for lefties as well meaning theres more space for your fingers.
Failing that the HW57 has a pop up breech, which is probably the easiest to load, but I've never tried one of these so can't really recommend it personally.
atvb
Bobs