Generally, you wont be able to find one. High switching frequency PSU chips strongly tend to be SMD only due to the need to shrink the loop area as much as possible to minimise radiated EMI and to avoid instability. That also means slapping a LT3461A on a generic TSOT23-6 to DIL breakout board isn't an option.
You can probably find something old fairly easily that switches in the 50KHz to 200KHz range in DIP or TO220-5 packages, but it will need *MUCH* larger and more expensive inductor and capacitors.
IMHO your best course of action would be to keep the section around the LT3461A surface mount. There's nothing there that's too tricky to hand solder, but if for example, it must be assembled by students, consider making it a small daughterboard following the recommended datasheet layout that can be preassembled by staff.