Actually, it's absolutely normal. Feeding a raw diet, which is entirely meat/bone/organ and completely digestible by the dog, produces much less "output". When a dog is kibble-fed, most ingredients in kibble are not digestible, like the grains, fruits/veggies, carbs, so these are completely excreted in the poo. With the introduction of bone, a fabulous stool firmer, it's completely normal for a newly raw fed dog to not poo for a couple of days. You could try feeding a bit less bone if you're concerned.
If there were an intestinal blockage, other symptoms would be in play. The dog would be acting ill, and be in pain. It wouldn't eat or drink, and may run a fever. It would probably also vomit, first foamy clear froth followed by bloody foam and perhaps even brown fluid. If the only "symptom" is no poo for 2 days, I wouldn't be quick to assume the worst

If the no poo thing continues for longer then 4 days or so, it would be worth further investigation.