The 'shoe capital' of Spain is Elche (Elx).

There are dozens of factories that sell direct to the public.

Elche is about 10km, and inland from Santa Pola. Which is about a 10 minute drive south from Alicante airport.
If you go into town and find one of the many tourist offices, they will direct you to the factories.

More info HERE

'Pikolinos' They manufacture the shoes and have a big showroom/shop. It is well worth a visit. The shoes they make are so comfortable they are like wearing gloves. They are not cheap, but very good quality. The only problem is - trying to decide - how many pairs you can afford