Do you reload? if you don't that will dictate what calibers you can convert to, here are a few that ammo is relatively available.

204 Ruger
223
22-250
220 swift

6BR
243

25-06
257WBY

260 Rem
264 WinMag
6.5 X 284

270 win
270WSM
270WBY

7-08
280
7mm RUM

308
30-06
300 WinMag
300 WBY
300 RUM

338 WinMag
338 RUM

Dean