Still working on your shopping list? Here’s how jewelers across the country are planning to fill their cases while they’re in Vegas.Finding new resources and ­scouting trends are top objectives for ­jewelers headed to JCK Las Vegas this month, but one issue is overshadowing the rest: the skyrocketing prices of gold, silver, and ­diamonds. At press time, gold had ­broken the $1,500-per-ounce mark as the weak dollar and concerns about debt and inflation spurred demand for alternative investments. Silver also reached a 31-year high. And rough diamond prices could go up 15 to 20 percent in the next two to three years as supply fails to meet surging demand, according to industry sources. The pressure of rising mining, energy, and labor costs isn’t helping matters.Supply constraints due to ­increasing global demand are a top concern. In China, for example, Chow Tai Fook plans to at