Visa help needed!

Hi! You cannot legally work in Belgium if you have entered the country on a Schengen Visa (the typical 90 days visa as you put it). Belgian employers are extremely reluctant to give work to foreigners illegally without proper paperwork. So it would be hard for you to find a company willing to employ you while you're on the wrong visa. It is because if caught they have to pay severe penalties.

This is how non-EU nationals generally get to work legally in Belgium :

You find a job with a Belgian company ->
This company applies for your work permit with its local government office ->
Company obtains the work permit and posts it to you ->
You receive this work permit ->
You apply for a work visa (D visa) with this permit (+ other paperwork) at the Belgium Embassy ->
Embassy sends your papers to local Belgium immigration office for verification ->
If paperwork is okay, the immigration office notifies the Embassy ->
Embassy grants work visa ->
You travel with work visa to Belgium ->
Register yourself at relevant immigration office as a working foreigner ->
Obtain residence permit based on employment and live happily

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As far as going to Germany to apply for Belgium work visa - that will not work either. The only way in which you could apply from Germany to get a work visa in Belgium was if you were staying in Germany on a long term visa (category D - it includes students, researches, family, workers etc.). This goes not only for Germany but all countries within the EU.

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US citizens can apply for work visa mail. This won't work for you - your passport would be with you in Europe and the Belgium Embassy will need it in USA to even begin the work visa process. If you're thinking that you'll courier your passport from say Belgium to USA for visa processing, then let me share that in my knowledge passports cannot be couriered internationally by common individuals like us.

Even if you somehow through friends or family arranged for a work visa to Belgium - you would still need to leave the Schengen territory and enter it again with a work visa to be able to work in Belgium. On what type of visa you entered Belgium would be fed in immigration systems.

I hope this helped. For further information on what paperwork you would need to apply for work visa, see the link -

http://bit.ly/1eNr8O3

By the way, if your home is in California, you'll need to apply at the Consulate General of Belgium in Los Angeles -

http://bit.ly/1D5TY2g