I know that the halacha is that you can't make a copy of the menorah with seven branches, and that you shouldn't have a candelabra with seven branches, either. What if it's made out of glass?
Rabbi Cohen of Dose of Halacha writes that it's ok:
The Gemara (Rosh Hashana 24a; Menachos 28b) writes that it is assur deoraisa to create a seven-branched candelabrum as the Torah (Shemos 20:20) forbids imitating any of the kelim of the mishkan.
The rishonim debate whether this applies to all seven-branched candelabra or just exact replicas of the original menora. The Bechor Shor (Rosh Hashana 24a) holds that any seven-branched candelabrum regardless of its size or shape, etc. is assur while Meiri (Rosh Hashana 24a) writes that if it is even slightly different from the original menora, then it is permitted (See Chacham Zvi 60). The Shulchan Aruch (YD 141:8) follows the Maharik (75) who writes that if it would be kosher bedieved in the mishkan then it is assur.
R’ Yosef Chaim Sonnenfeld (Salmas Chaim 272) writes that one shouldn’t even make a model of a menorah for educational reasons. R’ Moshe Feinstein (Igros Moshe YD 3:33), however, disagrees, writing that Rambam (Beis Habechira 7:10) allows one to make a seven-branched candelabrum out of wood or earthenware as such candelabra would not be fit as a menora in the mishkan (ibid 1:18).
Based on this, one would be able to buy such a candelabrum made out of glass.
As Zvi pointed out in the comments, glass is not kosher at all in the Beis Hamikdash. The gemara in Menachos 28b says that any metal is kosher, but not earthenware. Various commentaries say that bone or glass would be the same as earthenware.
Rabbi Akiva Eiger in Yoreh Deah 141(8) says that anything that is not kosher for the menorah in the Beis Hamikdash, is allowed to make for yourself. His example is a gold menorah with no cups, knobs, or flowers. This would be the same: Glass is fine.