Bike looks fine, very zedcred. Seems like you have g0t a good result for your labours – well done.
All you can do is ask the vendor the provenance of the brake shoes. If you are buying from one of the established dealers I doubt they have any NOS of consumables like brake shoes. These are most likely to crop up if at all from the occasional Ebay advert placed by someone who has found a few spares lying around the garage. In any event, I am not sure that linings deteriorate provided they have been stored properly and some modern linings can be a bit hard and take forever to bed in.
The better way to go if braking remains an issue is to use an ETZ front end with disk brake. There are some wrinkles on this which you should research but its pretty straightforward. You may find you can swap some of your surplus spares – worth asking anyway. Otherwise put them on Ebay.
best wishes
Peter
