Not 100% sure which hard line you need. The 2 from the t block on the diff cover to the wheel cylinders ? or hard line from the frame to flex hose ?
Yes you can replace the 2 lines, pre flared steel line with tube nut, can be bought at your local parts house. you will need to bend this as it will come straight sections, and come in different lengths. If possible remove your old one to use as samples at parts store.
If you need the frame to flex hose, that can to be replaced with longer section of pre flared, but will need more complex bends. If it were me I would try to replace the tube nut. Cutting the flare off slide off old nut, new like tube nut in it's place. Then make new double flare on the existing hard line. After that is done the line will be short and some minor bending, little swearing, and may be get your tongue stuck up your nose just right to get the tube nut to start in the flex line. Good luck. Also if you decide pre-bent lines are what you need, look at Inline Tube, they offer 20% discounts every so often, maybe sign up e mail for introductory discount code. Not sure if they do that, but they have good stuff.