This might be a late answer to your question but I was able to take the 30 atom rhombohedral lattice for corundum and turn it into a orthorhombic lattice pretty easily. I did it in a spreadsheet. If one of the a directions is along x and c is along z, double the cell in the y direction by adding a * cos(60) to the x-coordinates and a * sin(60) to the y-coordinates for each atom in the original cell. You should now have 60 atoms in your cell. Next reflect all the x coordinates back into your box. If one corner of your 60 atom set is located at 0,0 in x and y then just use an if statement like if x > a then x = x -a. Your new cell with be orthorhombic with dimensions of a, 2 a sin(60), c and will contain 60 instead of 30 atoms. You can then replicate it using whatever code you like, lammps, excel, etc.
Note: After much searching, I found the lattice online. I was not able to reproduce it from the space groups. I tried but then gave up.
Good luck, Dave.
PS. If you want a copy of the spread sheet, let me know.