Can I buy IP address from any webhosting or I must buy it from my provider?

You normally get them from your webhosting company, who gets them from the datacenter.

You usually have to buy them from your provider. Also, some providers ask for justification so you might have to tell why you need those (i.e. for which domain, if you need it for SSL, nameservers, etc).

And me i think that you can buy only from your provider.
Christos