The "beige" classic flap is not as uncommon as you might think. Before this year, I believe, black AND beige were considered the ONLY 2 non-seasonal classic flap colors. And if you were to ask any Chanel/classic flap collector, I have no doubt they have BOTH a black and a beige in their collection. I do.
I ADORE my jumbo beige clair classic flap in caviar leather w/SHW purchased this year. Yet my very first Chanel handbag was black. And I would not have wanted it any other way.
Something you might want to take more time to consider: the Chanel Boy Bag is not the Chanel Classic Flap (and vice versa). Some, including myself, prefer only one style over the other. Many enjoy both styles. Since your heart was set on a Boy w/ RHW and in black, you are aking a 180 degree turn by settling for a Classic Flap, in beige w/ GHW.
These handbags, whether brand-new OR pre-loved, are simply TOO expensive to just settle for. Continue to search, ask questions and conduct your own research before you settle for something that truly does not make your ❤️ heart ❤️ sing! Plus, working with more than just one single SA, if possible, and at various Chanel "locations", will increase your options significantly. Best of luck in your search.