You will get the best coupons directly from Pampers. As I recall, they were sort of pokey sending my first batch, too, but then they did well. The Pampers coupons are usually in the newspaper only in the Procter & Gamble insert, which is in the first Sunday of every month. I think that it's usually $1 off a package of diapers. The ones that Pampers sent me directly were more like $2 off.
The coupons that I received directly from Huggies were also more valuable than the ones in the newspaper.
If you have friends/family with toddlers, you can try offering to trade them the coupons for Pull-ups and other toddler products for the diaper coupons. My friends were more than willing to do that with me, and it saved me having to buy extra papers for just the one coupon.
You might also join a coupon train and get extra coupons from it, but they can be a little bit of work, and you might not have time for that once the baby has arrived.