Have you considered a cross-under style bitless? I have a Nurtural brand bridle and really like it. Their Biothane and Nylon bridles are affordable and come in sizes from mini to draft. You might want to check those out. Biothane Bitless bridle Nylon Bitless bridle
Otherwise, you might want to google "Draft Tack" and see if you can find any draft specific web sites. They might have side pulls available.