andrew-
i'm not sure why din is no longer used...
i have a manual light meter that uses the scheiner system
which isn't used anymore either. it makes sense that
we are in the digital age now and i wouldn't
be surprised if the folks in the store didn't know a lot about analog photography,
unless there is someone there over the age of 35-40, but even that person might not have any idea about DIN numbers.

does your new camera have a working light meter ? you can pick one up used
for not too much $$$, or you can guesstimate all your exposures ( what i tend to do )
it is pretty easy outdoors at least its called " sunny 16 " and all you need is your eyes, and a little experience.
you might also look for a black cat exposure guide http://www.blackcatphotoproducts.com/guide.html

for indoor/flash photography just use a thyroister flash and go by whatever the dial + guide numbers say,
you won't have any trouble because the thyroister stops the flash when the "electric eye" tells realizes enough light
has been burst out of the xenon tube. you just note the distance the subject is from the camera ( your lens will tell you that )
set the flash on the camera, set your fstop, and expose your film.

you can use a digital camera, and a safe-sync filter and want to experiment being meter-less and using a flash on THAT camera for practice you can do that easy ...
set it on manual, adjust the iso in the camera to whatever you want, and have fun ...
just make sure you have a safe-sync filter, some flash units have a high trigger voltage which will fry your digital camera.

john