You can buy Plum grade Imperial Epineuse in online stores (seed and seedlings).
$9.84 Espoma Company 7.5 lbs Greensand Gs10 Tree And Shrub Fertilizer
$25.50 Transplant Formula - For Use With Plants and Seeds Including; Vegetables, Herbs, Fruit Trees, Shrubs, and Perennials - Great For Container and Raised Bed Gardens - Fine Powder Supplies Trace Minerals, Soil Microbes, and Biostimulant Carbons
$17.29 Nelson Plant Food For All Flowering Plants Annuals Perennials Bulbs Shrubs Indoor Outdoor Granular Fertilizer Color Star 19-13-6 (4 LB)
$18.41 Myke TRE18 Tree and Shrub Growth Supplement Mycorrhiza, 1.4 Quarts
$55.61 Pro Trust Products Plant 15.6-Number 21-5-12 Tree and Shrub Prof Fertilizer
$51.75 Winchester Gardens Landscaper Pack Tree and Shrub Fertilizer Spikes, 15-10-9, 70 Spikes/Case