the new civic si transmission has the closest gear ratios compared to all of the transmissions with a 4.40 to 1 final drive. ideally, the jdm itr tranny with lsd and a 4.75 to 1 final drive would be your first choice, however, this transmission will cost around 1700 new and around 1100 used. therefore, i'd suggest you get a civic si transmission for around 600.

if you do plan on replacing your synchro's it will be expensive...and not worthwhile. however, if this is what you really want...then find someone who knows what they're doing. opening up a transmission isn't something you're average wrench monkey can usually do successfully.