Just to give you an idea about what is available you might like to take a look a Asa-Lift, Denmark (http://www.asa-lift.com/cms/en-gb/Frontpage.aspx), Simon, France (http://www.simon-online.fr/), Carlotti, Italy (http://www.carlotti-g.it/index.aspx?lng=ENG). For vegetable transplanters try the country flag links at (http://www.agmachine.com/ammd45e.htm). These units may be larger than you want but the principles will probably remain the same and can be adapted to a smaller scale. Clearly onions, and vegetables, require a good soil, a high standard of seedbed preparation, possibly pelleted seed, quality seed, and ideally precision planters. Hopefully this helps and others may have further ideas,