if you've been drinking your wine then a blood lead test will be very informative. Similarly for anyone else who has been drinking your wine. The more results the merrier. Please send all results with ages and genders of each person tested, and some rough idea of which person has drunk the most and the least of your wine and how they line up in between in order. If there's a trend - if the people who have imbibed the most of your wine have the higher blood lead levels, then you could easily justify testing the wine for lead, and finally testing the marbles for lead. This would need to be done at a lab although you may be lucky and find someone in a nearby environmental consultancy or health department has an XRF machine that you do a heavy metals screening test on the marbles. Heavy metals are the only class of toxic contaminants that are relatively easy to screen for and test at a lab. You'd have to ask the marble manufacturer whether the marbles contain any other toxics - there are too many toxics options with too many expensive test procedures (or no test available at all) to test for the 80,000 toxic chemicals that are known to be used today.
But your question about lead is a good one - because lead makes numerous pigments (with a wonderful array of colours from yellow to orange to red and therefore including green, purple, and brown), is known as an ingredient in glass-making, and is cheap so is typically used in unregulated countries whenever a more expensive ingredient would be used in a more regulated country.
If the marbles come up with no lead in the screening XRF then it tells you there's no lead in the surface or the surface coating (if they are indeed coated). XRF testing doesn't tell you whether there is lead in the main body of the marble, for that, the marble would need to be acid-digested for analysis at a lab. It is because lead is leached out of glass (and other substrates) by acid and by alcohol that it is particularly unwise to put any leaded thing in contact with wine. That's why lead foils were phased out on the outside (over the cork) of wine bottles, and that's why people should be advised never to store wine in lead crystal or ceramic, and never to squash their grapes in a (possibly leaded) ceramic bathtub. A case occurred in Australia where for several years, a bathtub winemaker went with worsening health problems to dozens of doctors before one of them tested his blood lead level (it was extremely high). That's why I go straight to the blood lead testing as my first recommendation.
I hope this helps and I'd love to get all and any test results, as would the health department, and probably winemakers organisations / bloggers / twitters etc - in case a warning needs to be sent out to others who