I am learning Norwegian but face the same problem. I can take the written Bergen test in London but would have to travel to Norway for the oral. So I am thinking of switching to Swedish because I can take the SWEDEX exams. I understand that in the USA you can do a test in Norwegian at the University of Central Florida. Not sure if this is only for their students or if externals can sit the exams. Might be worth checking out.
I'm not aware of any standardized test for the lower levels, either; Bergenstesten (higher level / B2 / C1) tends to be the one to aim for - but as you say, it really is quite advanced. It is indeed possible to take this test abroad, as I'm sure you have found when looking into it - so I guess you've already had a look at the relevant information that these links lead to:
Lykke til :)
Since Norwegian is such an unusual language with a few teachers, I don't think that there are any other standardized tests other than the one you mentioned. I've personally only heard about Bergenstesten, which, if I've understood correctly, you can only take here in Norway. Unless you physically come here I think your options are few in regards to having your Norwegian abilities assesed. Anyways, Bergenstesten comes in two difficulties, b2 and c1. I don't think you should come all the way here just for a potential b2. Have you looked into the possibilities of taking language courses or joining an exchange student program here in Norway? After a few years living here you would become pretty decent i think.
Siden Norsk er et ganske lite språk med få lærere, tror jeg ikke at valgmulighetene er så store. Av standardiserte språktester har jeg personlig bare hørt om Bergenstesten, som du kun kan ta i Norge, om jeg har forstått det riktig. Med andre ord, så må du nok dra til Norge for å få dine Norsk kunnskaper vurdert. Bergenstesten kommer i 2 ulike vanskelighetsgrader, b2 og c1. Jeg ville nok ikke dratt helt hit for å ta en b2 test. Har du sett på mulighetene til å være utvekslingsstudent/språkkurs her i Norge, jeg kan si deg så mye at i løpet av 2 eller 3 år her, så er du nok i stand til å forstå det meste.
Edit: For all i know, there might be some online courses that will give you a diploma or some papers. I'm not sure though. Check with the universities or community colleges here in Norway, to see if you could potentially sign up for an online course.