Dear Nenad, sorry to see that your very interesting question has not yet received any expert answers. Sodium germanate seems to be a bit uncommon. Here is some information about a Chinese supplier who sells sodium germanate:

https://www.chemsrc.com/en/SupplierProduct/12529-48-5_1632603.html

If someone at you department has a muffle furnace available, you can easily make sodium germanate yourself. A 1:1 mixture (molar ratio) of finely powdered Na2CO3 and GeO2 is heated in a platinum crucible to 1200 °C. Upon slow cooling inside the furnace, needle-like crystals of Na2GeO3 will form in high yield.

Good luck with your research and best wishes, Frank Edelmann

Dear Frank,

Thank you so much for helping,

Best regards

Nenad

Hi Nenad,

You may make an inquiry at Alfa Chemistry, they offer kinds of good-quality chemicals.

https://www.alfa-chemistry.com/inquiry

Dear Nenad L. Ignjatovic just in case that your interesting technical question is still of importance to you: When you search for commercial suppliers of sodium germanate on the internet, it might be a good idea to search for alternative names of this compound. For example, another common name of Na2GeO3 is "sodium metagermanate". When you search for this term, you will find for example the following potentially useful link:

Sodium Metagermanate

https://www.americanelements.com/sodium-metagermanate-12025-19-3

or

SODIUM METAGERMANATE, hydrate, 95%

https://www.gelest.com/product/GES6940/

and several other.

I hope this helps. Good luck with your research and best wishes, Frank Edelmann

Thank you for the information, it is very helpful.