No orphanages or zoos with chimps in Rwanda, as far as I know.
The only place in Rwanda where wild chimps live, is in Nyungwe National Park in the south, between Gikongoro and Cyangugu. In Nyungwe there are many primate species. Famous is a group of hundreds of black and white colobus. Since a couple of months you can do a canopy walk there. There are also treks offered to look for chimps. I havent done it, but chimp watching is not as breathtaking as gorilla watching, because you can see the gorillas from very close distance, only a couple of meters. With chimps you need more luck.
http://www.rwandatourism.com/nyungwe/?PHPSESSID=1c2549ea08537ee118f6de26e4c57dd7
this is from the site of the agency Amahoro Tours:
Day 3 – Nyungwe National Park is the largest block of montane forest in East or Central Africa and is an incredibly rich area of biodiversity but the reason for your visit today is the primates. With 13 species resident you report early in the morning to the Park’s offices before heading off to trek chimpanzee. Overnight Nyungwe
Day 4 – Returning to the National Park today you have the opportunity to do a nature walk, visiting Kamiranzovu waterfall. The forest comprises amongst many things at least 200 tree species, over 280 bird species and more than 100 different types of colourful butterfly. A true feast of the senses for the nature lover. Overnight Nyungwe