While many people are busy looking for the slightest hints of the vast scientific knowledge possessed by our Sages, I've bumped into Rasa"G's interpretation of Sefer Hayetzirah 4,2 (c.900) (is there an online translation?):
כי העולם ככפה והגלגל אינו זז ממקומו כי הוא העולם עומד תמיד והגלגל שבקוטב צפון ודרום העגלה לצד צפוני לעולם ואינו זז כדפירשתי:
And that looks to me like a very Flat Earth description of the world.
Are there other Rabbinical sources that support the idea of a Flat Earth?
I think this is another Rabbinical source which promotes the idea of a flat earth:
The Holy One, blessed be He, raised up all the waters of creation and set half of them in the firmament and half in the Ocean; it is surprising! It is thus written: The river of God is full of water. The firmament is similar to a pool [reservoir] and above the pool is a dome. (Bereishit Rabbah 4:4-5)
How can a dome cover a spherical earth and be attached to it at the same time? It only works with a flat circular earth IMO.
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.
All biblical and cuneiform texts "posit a flat, probably disk-shaped world. The heavens are made of solid material. They are ... dome-shaped, completely enclosing the surface of the earth." Moshe Simon-Shoshan, "The Heavens Proclaim the Glory of God: A Study in Rabbinic Cosmology," BDD 20 (2008): 70.
"[The ancient sages of Israel] believed that the earth is a roughly flat disc, and the rest of the universe is a hemispherical solid dome fixed above it." Natan Slifkin, The Sun’s Path at Night: The Revolution in Rabbinic Perspectives on the Ptolemaic Revolution (Jerusalem: Lander Institute, 2010), 4.
I've bumped into probably the last of this camp, Jacob ben Joseph Reischer in his Shvut Yaakov SHU"T (c.1730) (Part 3, Q. 20) writes angrily against Rambam and other followers of Aristo who try to shake the traditional Jewish Flat Earth approach (couldn't find it in the text form):
