OK thats great and all but practically none of that matters. The Comte de Provence can bitch all he wants, it won't do any good. The french had never bypassed a rightful heir at that point in history. Second, no one would recognize him as the rightful heir. No Royalist, nor foreign government. Louis XVII would be the rightful King, end of story. And the other problem would be who's the Comte's heir? The deposed Louis XVII? The Comte de Artois? Or the Duc d' Angouleme or de Berri? See screwing with the succession line would just cause all sorts of chaos and would unnecessarily divide the Royalists. No if Louis XVII doesn't get an equal bride, he'll just wait until he's restored, like de Berri did.
Might I remind you, Gaston would've had the same problem with the Fronde (his only son died in infancy, and he was left with five daughters). Though admittedly Louis XVIII is far more intelligent than Gaston. Richelieu once spoke of him [Gaston] as being like glass - IIRC.
Also, the only reason I can think of that Louis XVII
won't get an equal bride would be for one of two reasons:
a) It doesn't look like he'll be restored to the throne any time soon, or
b) Nobody wants to piss off the French government by providing him with one.
Berri
did go acourting during exile according to Susan Nagel. One of the places where he stopped was Naples. There he paid court to Maria Amelia (later Queen of the French) and her sister Maria Cristina (later Queen of Sardinia). However, AFAIK their father refused because of the volatile situation in France or somesuch (this was around the same time Angouleme married Madame Royale). So Berri returned to London and married one Amy Brown in 1806. Then at the Restauration he separated from her and the marriage was declared invalid due to lack of royal assent.
Therefore, I should imagine - if the royal family were putting pressure on the younger generation (Angouleme, Berri) to marry in the hopes of continuing the Bourbon line, the chances that they would allow Louis XVII to remain unwed is unlikely.
He would need a bride from a comparatively liberal (to the Bourbons, anyway) house, since you can't have him (or the government whou might want him to be a rubber stamp) being liberal, and then having a wife who's going to slip her feet under the table and bring up a brood of more conservative minded princes.
My opinions
Amelia of Britain/Alexandra/Elena/Maria Pavlovna is a good idea (if you could get anyone in either royal family or Parliament to agree to it).
Maria Amelia was too conservative (she had very established ideas of what and how royalty were to be)
I would say a German princess who is perhaps willing to find Paris worth a mass - i.e. Baden, Württemberg, Hesse; or who is already Catholic like Wittelsbach or Saxony (all married into, or were proposed to marry into the Bonaparte-Beauharnais family - except Saxony).
An Italian princess - Naples, Parma, Tuscany, Modena (all cousins) - is only to be considered in dire circumstances (since it wouldn't be deepening the gene pool any by allowing one of them to go to Paris [particularly Parma]).
An infanta (of Spain/Portugal) could sit comfortably as queen (the closest relative would be Louis XIV/XV or Friedrich August II of Saxony.)