A No. 4 Rifle bolt will do. You'll have to have it fitted for headspace. Not as big a deal as it is for most rifles, but can be more expensive. You need a bunch of bolt heads and a full set of headspace guages. Bolt heads are numbered 0 to 3. You'll need one of each at $19 each. Marstar has 0's to 2's. You might get lucky with one of them.
Marstar lists stripped bolts(just the body) at $39. You'll have to buy the rest of the parts separately. Not exactly cheap by the time you're finished. Cocking piece - $17. Firing pin - $18, its spring and screw are $8 and $5, respectively. Extractor is $14, its spring and screw are $8 and $7, respectively. $102 without the bolt head.
Gunparts, Stadeside list complete bolt assemblies at $70.35 US. You'll still need the bolt heads. They list stripped, original, No. 5 Rifle bolt bodys(has a hollow handle knob) at $51.10 US. You'll need all the internal parts.
Pricey, but the rifle is worthless without a bolt.