Advising guests where to buy clothes to for a stricter dress code?

If this is real and not pot stirring, please do not commit the faux pas of treating your guests like props as opposed to adults who can and should be allowed to dress themselves. If your wedding is truly a black tie affair, then you'd indicate "Black tie" on your invitations, but that is the extent of it. Beyond that you have absolutely no business telling people what color to wear or where to buy clothes. That's overstepping in a big way.

The fact that you are not having a bridal party has nothing to do with it.

Yikes - that is all a big no.

You're already overstepping by asking guests to dress in your wedding colors. Black tie itself is enough of an imposition on guests. Asking guests to also dress in your wedding colors is way over the top and presumptuous. Just say black tie and be done with it.

Telling people what color to wear is overstepping, telling them wear to shop is beyond overstepping. Simply list "Black Tie" on the invite and let people handle themselves. You can only do this if you are hosting a true black tie wedding with a top shelf open bar, live band, evening ceremony, etc.

I'm used to black tie events, and receiving a list of expected colors and preferred shops would make me think the host was amateur. You also risk alienating your guests expecting them to buy new clothes to enter your event. Just list black tie and expect adults can dress themselves.