Are you asking about the limit of sending friend requests, or do you want to get more requests because you want to be popular?
Have good content people will find interesting, interact with others and comment on their posts to get their attention (but don't be spammy). Basically, try to be friendly and try not to be annoying. Of course there's paid options where you can buy likes/friends. If simply "numbers" is your goal then google "buying fans on facebook" and you'll know what to do from there.
hey u posting everyday 2 or more pic in ur fb account and tags frnds. I am sure to say this is help to increase frndz.. try this...
More friend Request in one day may block you from Facebook use safe way for manage facebook you can send only known person in facebook.
I agree with this answer, and can add that try to make or create something really interesting and study your target audience and its needs.
If you just want to increase the number of friends fast then post in large pages .. You can write there to be added as friend. You'll get too many friends requests. Games like farmville and few others can also be used for this purpose.
Make your profile more attractive. You need to have an attractive display picture. Make interesting posts that would attract your current friends. If you friends share your links then others will see it too. Join groups and be very active over there. If you are active and friendly in groups, then other people will add you all the time.
You can buy them from different websites, try SEOclerks as there are many freelancers here which can provide you friend requests at a cheap rate.
I think by posting worth while feed and catching people's attention will get you noticed! Give them something they want to read!