In the middle of cooking Pad Thai and discovered I don't have any tamarind paste. !!! Substitutions?

Pomegranate molasses - surprisingly good substitute!

date (dried, syrup or paste) and some lemon juice

All the above will help - but start with a small amount and add to your tastes. BTW, HP sauce in the USA is similar to A1 - but use just a little bit. Tamarind is mostly bitter with a hint of sweet so do as you wish and don't tell your guests.

Worcestershire sauce is made with tamarind. Also HP sauce if you happen to have some. I think I ended up using brown sugar, vinegar and paprika one time as well.

Dried Mango powder could be an option

Oh no! You'll need to kick up the sweet/sour. How about lime juice and brown sugar?

Raisin, brown sugar and soy sauce in a mini prep? Or...fig jam, soy sauce.
Or grind up some fig newtons with some soy and fish sauce.

Try lime or lemon juice, plus an optional spoon of ketchup.