I left my cpap equipment in the states. As a United States citizen can I buy tubes and masks in Germany? Anyone have knowledge of rules or laws in Germany. Or how to purchase?
Anyone have knowledge of rules or laws in Germany
Not I, but I would go to a pharmacy and see if you can get what you need. If they cannot provide/sell it they may be able to tell you how to go about it.
Can someone in US ship yours to you? Probably not cheap, but if essential, its an option.
Without knowing this special case I would say that you will find / get it at every "Apotheke" (pharmacy) which are separated shops in Germany - not in super markets or drugstores ("Drogerien").
Be aware that very often EU and US products have different sizes and tech specifications for connectors and adapters, also for electric power (see #12).
Just to get an impression you can check a German online pharmacy (e.g. DocMorris or Versandapo) and try to search for your needed products (e.g. "Atemmaske").