Is there an office somewhere, where I could purchase the Gold Units, or discuss any issue? 

Yes.

While GGMF does not maintain physical offices where customers can interact, INSTEAD, GGMF licences banks, financial institutions and entrepreneurs to provide financial services to the public, Sovereign Individuals, corporations, etc. for which they are paid a three percent (3%) fee for providing such services, including the resolution of any issues and the conversion of FIAT currencies by banks.