Hi there are a few rescue centres that have schnauzers for rehoming - though often you need to have a resident dog to help them settle but have a look at these sites (there are probably others but I know these have some)
www.manytearsrescue.org (search under 'schnauzer' to bring all up.
www.msri.ie
www.prodogsdirect.org.uk
www.dbarc.org.uk
god luck in your search
Cyril and Beryl (mini schnauzers) and Izzy their mum