You ask if there are other Rabbinical sources that support the idea of a Flat Earth? there are some, though they are few.
Whether or not some sages believed in the geocentric view - the sun revolving around the earth or the heliocentric view - the reverse, we still describe our evenings as “sunset”. Our perspectives are based on our assertions which is decided by looking to the horizon.
It has been noted that since antiquity, the Greeks recognized the heliocentric and not the geocentric view, which was the consensus at the time. However, since the antiquity of its history, the Church knew it was round and the size of its circumference. While most Talmudic rabbis endorsed the heliocentric view, there were some who engaged in the geocentric. Of course, the sun’s position is relative to each standing perceptive.
In Ri of Barcelona’s commentary on Sefer Yetzirah (p. 254a), he quotes Rav Saadia Gaon supporting the theory that the earth is flat. This was a minority (miktzat) opinion. Another was Rabbi Yehuda HaNassi who said the underground streams were cold because the sun traveled beneath the earth at night and that this theory seemed more correct. Some Jews believed the sun traveled above, indicating a more flat earth theory. The Lubavitcher, Rabbi Menachem M. Schneerson, of Chabad wrote in a correspondence to a friend of the nonsensical notion that the sun and earth change positions based on the merits or sins of the Jews. Obviously, this nonsensical notion is ridiculed. Magic, demons, and ghost do not exist. They have never been proven and thus belong to the fabrication of the wild imagination of the mystics to support their emotional needs. Maimonides said that some ancient rabbis were little experts in the realms of science and did not always fully understood how the laws of nature worked (Guide to the Perplexed, III:14). For the rationalist, Gersonides (Ragbag), Maimonides (Rambam), and Ibn Ezra were convinced that the sun did not stand still for Joshua nor did the sun’s shadow move ten degrees backward on Hezekiah’s deathbed.
In summary, a few rabbis in the Talmud believed it was flat and some were unsure. In spite of that, the majority knew it had to be round, which was proven by modern science today.