Although a machine shop is fully capable of pressing in new ball joints, you should be able to go to most any automotive garage/service center. A "shop press" is a fairly common piece of equipment in most garages around here.
Think about it.... 75% of the people needing new ball joints on their truck drop it off at the shop to get fixed. The shop pops the old ball joints out and presses the new ones in.... they don't "farm" this aspect of the repair process out to a machine shop, they do it in house.