depending on what you need you can do a few things. a book of shadows is just a notebook. when i started, i used an old hard cover sketchbook i never used and was collecting dust. now i've got a few others, and use fancier books for certain ones. [my book of rituals has gold edged pages for example] find one you feel works best for you and use it.
herbs, flowers, plants, wands, and other similar items can be found/made from what lives in your area. my first wand was made from a branch i took off my favourite lilac in my back yard. there's a process many wiccan's go through by befriending the plant, asking for permission and leaving an offering. i'm not sure though if other pagan paths do this, so research the process of your path before yanking leaves off a bush for a spell.
crystals, cauldrons, and other hard to find object that can't be made by most people can be bought at occult shops, and/or certain stores. a mortar and pestol can be found at a cooking store for example. your athame can be any dark handled two sided blade [could be a letter open for instance]
or, if you just want to get started and buy all these items [i do suggest taking your time and slowly building your magickal collection] there is an online store on SoM:
i've never bought from it, but i do occasionally window shop, they've got a lot of nice items, just watch your price and don't go crazy. [that goes for offline occult shops as well]