Are you ONLY interested in conformation? An altered purebred Mal can compete in AKC obedience, agility and most other performance events with an ILP. And yes- any reputable rescue organization will spay/neuter their animals before adopting them out.
To find a dog suitable for conformation competitions- you'll need to find a great breeder and sit on a waiting list. For a loooong time, in many cases. The biggest upside is- you'll have a mentor who can "hold your hand" and give you pointers, perhaps co-owning. The biggest downside is the financial strain of acquiring a show quality dog.
Your best bet, IMHO- is to leave conformation alone for now and look into the performance events. Rescues often get the PERFECT dogs for agility and obedience trials- adolescent dogs with tons of drive who NEED someone to work them- it's the lack of brainy stimulus that manifests as the "bad behavior" that gets a dog turned in in the first place. Will you be able to find a purebred Mal puppy through a rescue? Sure- if you're VERY patient and not picky whatsoever. Puppies go fast- purebred puppies even more quickly- and the waiting lists for them are always long. So that's why you might want to concentrate on getting a YOUNG dog- not a puppy.