Hi, and Welcome!
Your T264SR is a popular model. The model was introduced in 2004 and remained available until the end of 2007. It was the T260SR the year before. I bring this model year up, as the 2004-2007 models used the Lippert Components electric rack-and-pinion slide drive system. The older camper used other brands of slide drives.
What you show in your picture is two parts, and I'm not sure which one you are after: the upper part that bolts to the slide room floor, or the bottom part that bolts to the slide drive arm. Both are manufactured by the same company, Lippert Components (LCI), for short.
You can go directly to them for parts. I suggest you call them and confirm the correct size, as Sunline used the larger slide drive arms than many new campers do today. Measure the square size of the slide arm; I think it may be a 2 1/2 x 2 1/2" square tube, but check before you call. And you need to measure the drop below the bottom of the slide arm, as they offer different drop sizes.
Here is the LCI direct parts store site. There are 25 pages of slide parts.
RV Slide-Out Parts | Lippert
The lower part of the slide arm is called a "V-tech drop head," and the height of the drop. This one is 1 3/8" drop that fits on a 2.5" x 2.5 " slide arm.
V-Tech 1-3/8" Drop Head Assembly - Fixed | Lippert
Here is a flush one, no drop. I'm showing this so you know to measure yours before calling.
V-Tech Flush Head Assembly - Fixed | Lippert
NOTE: There are two styles of those V-tech head assemblies. The head of the motor drive slide arm is fixed. The head of the auxiliary slide arm is slotted and adjustable.
Here is an adjustable flush head
V-Tech Flush Head Assembly - Adjustable | Lippert. The adjustable head is used to adjust the location of the auxiliary slide arm in and out of the camper.
Know which slide arm you need the head for. To recap.
1. Measure the square tube size of the slide arm.
2. Measure the drop below the bottom of the tube to which the adjusting nut is welded.
3. Ensure you select the correct head, which is located at the motor slide arm of the auxiliary slide arm.
4. You have an Electric rack and pinion slide drive by LCI
The top part in your picture that bolts to the bottom of the slide floor is called a V-tech head assembly, which resembles this. Again, it goes by the arm square tube size.. Measure yours to make sure it will fit. I'm not sure if this is accurate for your camper, but it appears to be close. It says 'hydraulic slide,' not 'electric slide,' which yours is.
V-Tech Head Assembly with 12" Room Bar | Lippert
This one says, electric and hydraulic
Head with 12'' Room Bar | Lippert
Call them, they are helpful. I have bought directly from them in the past, and they have been helpful. They will not know what your Sunline has; they only built the slide drive, and Sunline installed it. However, if you measure what you have and they can send you a sketch of the correct ones, you can confirm before buying that you are getting the right parts.
Let us know how you make out. And let us know which part numbers are correct, as this information can help someone in the future. You are the first to ask for those parts. I have worked on these Sunline slide drives, but never had to replace one of those V-tech head assemblies.
I hope this helps.
John