I've actually substituted lime juice for tamarind before and although the taste is a little different, it still comes across as a tasty pad thai!

Awesome, good to know! Thanks.

There are no real substitutes for either of those sauces, although you can dilute the tamarind paste. The fish sauce is a distinctive Thai flavor and necessary for authentic Thai dishes. You could make Pad Thai without them, and it could be very tasty, but it wouldn't be pad thai. The good news is that those spices are quite commonplace, and can easily be ordered over the internet. For instance, Amazon has a huge selection of Thai spices and condiments.

Our Safeway actually now sells the pods in the vegetable section. Have you looked? You take out the seeds, soak in hot water and push the goo through a strainer. But we have also purchased a whole block of seeds and pulp which lasts in the fridge for a really long time- longer, it seems, than the jars of concentrate.

To be honest, I've never used tamarind in pad thai. Not to say it can't / shouldn't be done, but you can definitely make a good one without it and not miss it. Compensate with fish sauce, lime juice & brown (or, more traditionally, palm) sugar to taste.