I am a bit of a sword geek so I usually reccommend sword stores. There are several online with a huge range of pricings though so to make sure you got good value (and a properly constructed blade) I suggest a tad bit of research if you want to go that route.
A great starting place is an online free magazine and review site called sword buyer's guide. (http://www.sword-buyers-guide.com ) it has several articles on safety, guidance on what makes a quality item versus a 'wall hanger', why one should never, ever, -ever- buy a rat-tail tang, and also has a huge listing of swords and historic blades all ranging in $300.00 or less. They also cite other businesses that sell a variety of good products including daggers that would make lovely athames. here are a couple favorites:
Kult of Athena; http://kultofathena.com/daggers.asp Excellent prices, historical design, and are respectable quality.
True swords; http://www.trueswords.com/knives-c-58.html Much more modern in design, a lot of it from united cutlery and cold steel. Both are trustworthy names.
I am lucky enough to have a local cutlery store that also carries a variety of knives and swords (and spears and axes and clubs and... ) to keep me drooling over sharp pointy objects. it is a Canadian company, but has an option to shop online as well. They don't seem to have an option for shipping across the border, but if you have a friend in british Columbia you might be able to pick it up with a short road trip. ...Just be sure to check with customs first to make sure it is legal to bring it back across before you do any buying.
They have a huge selection so it might take some hunting. but if you find a gem you like, they usually include the maker so you can hunt the original manufacturer and order direct. here is one I kinda want to get for myself; https://store.cuttingedgecutleryco.com/product/damascus-rosewood-dagger-fixed-blade-9-5-dm1104/
You don't an athame if your unable to find one. You could use a kitchen knife as long as you cleanse it and consecrate it before using it of course. In my experience I've used my pointer finger and it's worked for me. You also don't need tools as Wicca or any kind of spirituality is about the spiritual side, not the physical.
Hello, Californian here.
I've not seen issues trying to get an athame just because of what it is. I've gotten blades from smoke shops (tobacco) that would have been great as an athame. Shipping online is probably difficult because it's a weapon. California has some strict weapon laws. The large the smoke shop the more chance of them having something.
You could try thrift type stores if you're not old enough for a shop. Just extra focus on cleansing if you go around thrift shops. Or yard sales.