I think what you mean is something like, 本当に世話になりましてありがとうございました。 Or
課長と話しまして事務室を出ました。 As for -desu, something like 静かでして穏やかです。 If this is what you are asking about, then it is just a way to be more polite with the -te/de form. The reason it may not be explicitly taught or discussed in grammar sections may be because -masu and -desu are an auxiliary and copula verb, and they conjugate like a pair of うーverbs ending with ーす, thus ーました and －でした。Tae-san, correct me if I'm wrong here, but I think you can use this more polite -te form with any grammar using -te, though in most cases other than as a chronological conjunction, it is uncommon, and a bit odd-sounding.
I think what you mean is
I think what you mean is something like, 本当に世話になりましてありがとうございました。 Or
課長と話しまして事務室を出ました。 As for -desu, something like 静かでして穏やかです。 If this is what you are asking about, then it is just a way to be more polite with the -te/de form. The reason it may not be explicitly taught or discussed in grammar sections may be because -masu and -desu are an auxiliary and copula verb, and they conjugate like a pair of うーverbs ending with ーす, thus ーました and －でした。Tae-san, correct me if I'm wrong here, but I think you can use this more polite -te form with any grammar using -te, though in most cases other than as a chronological conjunction, it is uncommon, and a bit odd-sounding.