Maybe look at the N70? There's maybe a model in the non-N-Series series that plays similar, but the ones I have don't play like a NS9900.
N70 is head heavy, NS9900 is headlight, the only similarity is their stiff shaft. The closest Li Ning N series is N33, but the shaft is not as stiff as that of NS9900.
TS, you may want to drop by Li Ning at ION, they have all the models there. I used to own a NS9900 but now change to NS9000 because of its more flex shaft. Otherwise, both are very fast racquetes. I happend to be in ION last weekend and I spent lots of time in Li Ning's shop. Let me share with you my presonal view(please note this is really very personal view). NS9900, very fast racket, stiff shaft, balance point 285mm. Weakness, not as powerful as one would prefer. The three Li Ning double Nseries racquetes are N77, N33 and N50. N77 is used by their women double players, so the shaft is flex and the racket is quite light. This model is nowhere similar to NS9900. N33 is used by Cai Yun, shaft is moderately flex towards stiff, balance point at 290mm. This is probably the closest model to NS9900 but shaft is not as stiff. N50 is used by Fu HF, shaft is stiff, balance point at 295mm, which makes it more head heavy than NS9900. Good for attack but for sure not as fast as NS9900 due to its higher BP. If you are looking for a comparable Li Ning model, I think there is none. If you are looking for one that is fast, NS9900 should still be the choice. but if you want power, N50 should be more powerful than NS9900. As I said, you may want to go try it out yourself. By the way, if you place $20, you get to test a racquete for a week. If you dont like it, bring it back after 3 days or so, exchange it with a diff model and test it out at no additional cost. I am not a Li Ning sales person, I happened to be there last weekend to have learned enough from their friendly sales person. I decided to stick to my NS9000.