
If the puppy is only 6.5 weeks, it's WAY too soon to panic about a testicle(s?) that hasn't appeared yet. Yes I like to see them by 10 weeks, but it's not unknown for a puppy going into the ring at 6 MONTHs, to retract a testicle!! Embarrassing, but not unknown.
Hang onto your money - scanning for this, at this tender age is pointless. I don't know whether this can even be done. Having a breed who, even at the time I let mine go home (usually 10 weeks) I can only pick those showing 'potential' to run on and not sell, I'd suggest you have a ways to go yet, before panicking about 'missing' testicles.