Attached you’ll find a photo from a u.fl antenna I made during the Christmas holidays to get the core running while I was waiting for shipment of my ordered once.
I just took a green marked cannula, cutted the intravenous end, and reopened the cutted end it with another smooth press prependicular to the first cut. Matched perfected on the center pin of the coax connector and helped me getting started with the Spark Cores during the Christmas holidays.
EDIT: take a file or sandpaper, place it on the table and grind down the cannula between your fingers until it has a more round shape to not to damage the u.fl connector with too much press on it.
Connects to my router 15 ft. away thru a concrete ceiling.
This is of course a temporary solution, but available at your drugstore, or ask your country doctor for help
Keep it out of the reach of children!