I have a manual bandsaw mill and it is actually quite easy to replicate the look of U&D sawn on manual mills. I too discovered it after throwing a blade off which resulted in 3 bent teeth. Since then I have actually tried to replicate this rough sawn look for a couple projects and it looks quite convincing.
The best way I found was to saw the timber with a good blade so the cut is straight smooth and sqaure and of the desired dimension. Then remove the timber and the good blade. Install an old blade and overset a couple teeth on the downward side of the band. Put a slab of scrap lumber on the saw and lower the blade until it bearely touches the surface of the wood. Drag the saw backward (careful not to knock the band off doing this) for a fuzzy textured cut. Pushing it forward makes a cleaner defined groove cut but it may have a tendency to dig in if you aren't careful . Make a few practice runs. The lower the saw blade the deeper the grooves, the more hooked the tooth is the narrower the groove. Once you've got the hang of it put on the timber.
For some other interesting effects the log can be dogged at a slight angle on the bed for one pass to replicate a pit sawn look. Making a second pass at the opposite angle creates a cross hatch pattern sometimes seen in hand sawn lumber or in that sawn on really large circular mills where curve is not discernable and the blade dragged a little exiting the timber.
As for patina, it depends what color you are looking for. A photo of what you are trying to reproduce would be very helpful. Black and grey colors can be had with water, chemicals and metals. Browns and reds come with oils and UV exposure. Wear marks or a few rusty bent nails can lend a lot of credibility to making timber look old too.
