The most widely distributed two-wheel tractors in North America are made by the Italian company BCS. I recommend Model 853, as most 30-inch tools can be installed on it.The 732 and 739 models have shorter handlebars (less operator leverage on the machine, especially a problem with heavier implements like the Power Harrow). Most importantly, only the 853 will have enough power to handle the 34” flail mower that should be used on 30″ bed systems. I would NOT get a Diesel engine, as they are more expensive and super loud...
BCS two-wheel tractors are equipped with a rototiller, but there is a wide variety of other attachments available. For bed preparation my equipment of choice is a 30" rotary power harrow (often just called a power harrow) which I would recommend over any other tilling or spading device. We also rely on a 34″ flail mower for dealing with cover crops and a Berta Plow (also referred to as a rotary plow) to create our raised beds. BCS America's web site is filled with all the info about walking tractors and implements. The site will point you to a local dealer near you. www.bcsamerica.com
Another supplier I like is Earth Tools, a family-owned company from Kentucky who has been pushing two-wheel tractors for market gardening for more than 30 years. and also sell implements from different Italian manufacturers like the R2 power harrow from Rinaldi & Berta flail mowers I like and use. They know their stuff more then anyone. Check them out at www.earthtoolsbcs.com