I don't see an all in one cable, the 10-50 seems to be a somewhat orphan plug. You could easily make one though(if you're so inclined).
Purchase:
https://www.amazon.com/Legrand-Pass-Seymour-3861CC5-30-Amp-250-volt/dp/B000BPFZHM/ref=sr_1_1?ie=UTF8&qid=1495797142&sr=8-1&keywords=nema+10-50p
and:
A 1' piece of 10 gauge 3-wire stranded cable and wire it to a 6-30r:
https://www.amazon.com/dp/B0095GKC8U/ref=sxr_rr_xsim_2?pf_rd_m=ATVPDKIKX0DER&pf_rd_p=3008523062&pd_rd_wg=aXXXC&pf_rd_r=X8272DM8BN6HY9DZ8MMZ&pf_rd_s=desktop-rhs-carousels&pf_rd_t=301&pd_rd_i=B0095GKC8U&pd_rd_w=xYRFV&pf_rd_i=nema+10-50p&pd_rd_r=QW9QDA1MF1VYEP379SE0&ie=UTF8&qid=1495797142&sr=2
Home Depot sells bulk cable for wiring the two together, hot to hot, hot to hot and finally ground/neutral to ground. Easy peasy, probably not much more than $30 for parts, much cheaper than replacing the outlet/wiring.
It would cost a bit more but you'd have a molded end on the L6-30r and you wouldn't have to purchase the bulk wiring, just cut off the L6-30p and wire on the 10-50p plug above, would add ~$12 to the total cost:
https://www.amazon.com/NEMA-L6-30-Extension-Power-Cord/dp/B00H3PM3D2/ref=sr_1_45?ie=UTF8&qid=1495799931&sr=8-45&keywords=nema+l6-30+extension+cord
Purchase:
https://www.amazon.com/Legrand-Pass-Seymour-3861CC5-30-Amp-250-volt/dp/B000BPFZHM/ref=sr_1_1?ie=UTF8&qid=1495797142&sr=8-1&keywords=nema+10-50p
and:
A 1' piece of 10 gauge 3-wire stranded cable and wire it to a 6-30r:
https://www.amazon.com/dp/B0095GKC8U/ref=sxr_rr_xsim_2?pf_rd_m=ATVPDKIKX0DER&pf_rd_p=3008523062&pd_rd_wg=aXXXC&pf_rd_r=X8272DM8BN6HY9DZ8MMZ&pf_rd_s=desktop-rhs-carousels&pf_rd_t=301&pd_rd_i=B0095GKC8U&pd_rd_w=xYRFV&pf_rd_i=nema+10-50p&pd_rd_r=QW9QDA1MF1VYEP379SE0&ie=UTF8&qid=1495797142&sr=2
Home Depot sells bulk cable for wiring the two together, hot to hot, hot to hot and finally ground/neutral to ground. Easy peasy, probably not much more than $30 for parts, much cheaper than replacing the outlet/wiring.
It would cost a bit more but you'd have a molded end on the L6-30r and you wouldn't have to purchase the bulk wiring, just cut off the L6-30p and wire on the 10-50p plug above, would add ~$12 to the total cost:
https://www.amazon.com/NEMA-L6-30-Extension-Power-Cord/dp/B00H3PM3D2/ref=sr_1_45?ie=UTF8&qid=1495799931&sr=8-45&keywords=nema+l6-30+extension+cord