Copying this over from an older post asking the same question. Not sure if the pricing is still the same, but in your case you would just want the gold switches and springs anyways since you already have the sticks:
Not sure if this reply comes way too late, but Happ actually sells a "Williams Modified" Competition Joystick. You can find it on their site, but some vendors can actually get them for you cheaper than you can get them yourself. They come with gold microswitches with a higher actuation point, as well as harder springs. Basically they were the ones Williams used for their Mortal Kombat Games. The diagonals are way easier to hit, as that is critical for those games. I have them for my MAME project that I am finally getting back into working on, and my friend has had them on his MK/MAME cab for years. They are perfect!
The modified ones are $21.75 instead of the $14.99 for normal Competition sticks from HAPP directly, but as I said, some industry vendors can get them for your cheaper. Arcadeemulator.net was able to order them for me cheaper. Check it out here:
http://na.suzohapp.com/all_catalogs/joysticks/50-6071-16Part # 50-6071-16
You can also just buy the gold switches and the hard spring, swap them out yourself, and biggitty bam, you got yourself a true MK arcade fighter stick with good diagonals.