Is it possible that I get a tourist visa for China in Seoul via an agency?

Why not apply for the visa in Netherlands ahead of your trip? As I know, most oversea Chinese embassies and consulates has stopped issue visas to temporary visitors in the country. However, you can still have a try to confirm with one of the agencies listed here http://www.chinaemb.or.kr/chn/lsqz/ls_qz/ls_qz_13/t229558.htm

Personally, I still advise you get the visa in your home country beforehand.

Thanks for the fast reply!
I'm not in Holland now, but in China. My visa is just valid until the 13th of december, but want to stay here until march. Already been to hong kong, want to try another country now :)
Do you know if those agencies on the list can provide a tourist visa in 2 working days?

If you do not have Alien Registration Card valid for 6 months in Korea, you are not able to get one there.
Do you mean you did try to apply from HK, but the service was not available there? then, you'd better visit the local PSB for extension or contact a visa agency for the latest information.

Thanks for the information!
I just wanted to go to another country to get my Chinese visa, because I've already been in Hong kong. But now I know I cannot go to Korea.
Thanks! :)